Low-Cost Lithography

ABSTRACT

The low-cost lithography disclosed in the present invention lowers the lithographic cost by improving the mask re-usability, e.g. by using programmable litho-system and/or logic litho-system. The programmable litho-system, with an opening-programmable mask, can adjust its image patterns based on configuration data. The logic litho-system can combine image patterns from at least two mask regions into a single image on a wafer or a mask blank.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a division of U.S. patent application Ser.No. 10/230,610, Filed Aug. 28, 2002. Said patent application Ser. No.10/230,610 is related to the following domestic patent applications:

-   -   1. “Opening-Programmable Integrated Circuits”, provisional        application Ser. No. 60/326,919, filed on Oct. 2, 2001;    -   2. “Litho-Programmable Integrated Circuits”, provisional        application Ser. No. 60/339,334, filed on Dec. 13, 2001;    -   3. “Low-Cost Lithography”, provisional application Ser. No.        60/395,099, filed on Jul. 10, 2002,

and the following foreign patent applications:

-   -   1. “Design of Three-Dimensional Read-Only Memory”, CHINA P. R.,        patent application Ser. No. 02113333.6, filed on Feb. 5, 2002;    -   2. “Programmable Litho-System and Applications”, CHINA P. R.,        patent application Ser. No. 02113475.8, filed on Mar. 20, 2002;    -   3. “Logic Litho-System and Applications”, CHINA P. R., patent        application Ser. No. 02113476.6, filed on Mar. 20, 2002;    -   4. “Design, Fabrication and Business Model of Litho-Programmable        Integrated Circuits”, CHINA P. R., patent application Ser. No.        02113477.4, filed on Mar. 20, 2002;    -   5. “Methods to Lower the Mask Cost in an Integrated Circuit”,        CHINA P. R., patent application Ser. No. 02113792.7, filed on        May 28, 2002;    -   6. “Logic Litho-System”, CHINA P. R., patent application Ser.        No. 02113836.2, filed on Jun. 6, 2002;    -   7. “Litho-Programmable Application Specific Integrated        Circuits”, CHINA P. R., patent application Ser. No. 02133303.3,        filed on Jun. 18, 2002,

all by the same inventor.

BACKGROUND

1. Technical Field of the Invention

The present invention relates to the field of integrated circuits, andmore particularly to low-cost lithography.

2. Related Arts

Lithography is the process of creating patterns in an IC layer. Itinvolves mask fabrication, lithographic and related processes. With theadvancement of integrated circuits, masks become more and moreexpensive. At the 0.13 μm node, a conventional mask costs ˜$30,000, andwell over $100,000 for a phase-shift mask (PSM); a typical mask setcosts ˜$1 million. For medium- to small-volume production, mask costbecomes a significant portion of the overall IC cost. The presentinvention particularly addresses the lithographic costs associated withopening-related patterns (e.g. inter-level connection andsegmented-line), high-precision mask (e.g. OPC-mask and PSM), SCIC(semi-custom IC) and ASIC (application-specific IC), and others.

Before proceeding further, a clarification needs to be made here: thesize, dimension, width, length used throughout this disclosure could beeither a size, dimension, width, length on wafer, or a size, dimension,width, length on mask. They are, in general, not specified, but shouldbecome apparent from the context. For example, no extra efforts havebeen made to distinguish the minimum feature size on wafer Fw from thecorresponding minimum feature size on mask Fm (Fm=Fw×R, where R is theimage-reduction ratio of the reduction stepper). They are both referredto as F throughout this disclosure. In the context of wafer pattern(patterns on wafer), F means Fw; in the context of mask pattern(patterns on mask), F means Fm.

1. Opening-Related Patterns

Opening-related pattern refers to the pattern at which an opening isformed in the photoresist during its manufacturing process. There aremany types of opening-related patterns in an integrated circuit. Themost common ones are inter-level connections and segmented-lines.

FIGS. 1A-1B illustrate a conventional inter-level connection (i.e.physical connection 50 va between upper- and lower-metal lines 162,174). It is a 1F-via 50 va, i.e. its dimension (Dv) is equal to or lessthan 1F, which is the minimum width (Dm, Dl) of metal lines 162, 174.The 1F-via requires precise control over the shape of the opening on themask (mask opening). Accordingly, the mask fabrication needs expensiveequipment (e.g. e-beam writing). In addition, this type of bordered via(i.e. via 50 va is completely encompassed by the overlapping area ofmetal lines 162, 174) has small overlay tolerance. It incurs a highprocessing cost.

FIG. 1BB illustrates a segmented-line 161S. As a comparison, acontinuous line 161C is illustrated in FIG. 1BA. This segmented-line161S comprises two segments 161′, 161″ separated by a segment-gap 161 g.This segment-gap 161 g is, in fact, a form of opening (referring to FIG.26). Note that the segments 161′, 161″ have the same width and if thesegment 161′ is extended to the right, it preferably coincides with thesegment 161″.

2. High-Precision Mask

High-precision masks such as OPC-mask (optical proximity correction) andPSM (phase-shift mask) are developed to extend optical lithographybeyond the range of conventional imaging. Both provide the first-ordercorrectional structures to mask patterns. The OPC adds serifs to maskfeatures to recover the loss of shape fidelity due to diffraction andthe PSM adds phase-shifter to mask features in such a way that patterndiffraction is partly cancelled. As a result, the imaged wafer patternshave more desired shapes. The correctional structures used by the OPCand the PSM are in direct contact with the zero-order pattern (the maskpattern that forms the majority portion the wafer pattern). Details onOPC and PSM can be found on “Silicon Processing for the VLSI Era”, Vol.1, 2nd Ed., by Wolf and Tauber, pp. 628-37. Both techniques addsignificant cost to lithography.

3. Semi-Custom Integrated Circuit (SCIC)

In an SCIC, customers are only involved in the design of a limitednumber of layers. SCIC manufacturers stock a large number of basewafers. On base wafers, only transistor patterns are finished.Interconnects between transistors are not processed until customerinputs are received. There are two key concepts in SCIC: one is SCICfamily; the other is SCIC product. A SCIC family comprises a number ofSCIC products. In a SCIC product, all chips have the same transistor andinterconnect patterns; in a SCIC family, all SCIC products have the sametransistor pattern, but chips from different SCIC products may havedifferent interconnect pattern. The patterns used in SCIC include commonpatterns and custom patterns: the common patterns are shared in a SCICfamily and created by common masks; the custom patterns are only used ina single SCIC product and conventionally created by custom masks. In thememory world, one exemplary SCIC is read-only memory (ROM); in the logicworld, one exemplary SCIC is programmable gate-array (PGA).

In a ROM, memory cell could be located at the intersection of horizontaland vertical metal lines. The bit stored in a memory cell is representedthrough the existence or absence of a via. Accordingly, vias arereferred to as info-vias. The via configurations of FIGS. 1CA-1CB, ifused in ROM, represent two ROM products: in FIG. 1CA, ROM cells 93, 94represent “0”, “1”, whereas, “1”, “0” in FIG. 1CB. One ROM of particularinterest is three-dimensional read-only memory (3D-ROM), which isdisclosed in U.S. Pat. No. 5,835,396. In the 3D-ROM, there is a 3D-ROMlayer (a.k.a. quasi-conduction layer) between said vertical andhorizontal lines (referring to FIG. 4 of U.S. Pat. No. 5,835,396).

In PGA, the connections between metal lines are configured by vias.Accordingly, vias are referred to as config-vias. If used in PGA, thevia configuration of FIGS. 1CA-1CB creates two metal connections: inFIG. 1CA, horizontal line 162 is connected with vertical line 174,whereas, in FIG. 1CB, it is connected with vertical line 173.

In PGA, routings can be configured through metal-line segmentation. Forexample, if the metal mask of FIG. 1BB is used, the gap 161 g willsegment the metal line 161S into two segments 161′, 161″, each of whichcan be used for separate routing and has smaller capacitive load; on theother hand, if the metal mask of FIG. 1BA is used, the metal line 161Cwill be a continuous line. The metal lines of FIGS. 1BA-1BB can be usedin different configurations.

4. Application-Specific Integrated Circuit (ASIC)

In general, ASIC is small and fast. In prior arts, all masks used in anASIC product are custom masks. The large number of custom masks makesmedium- to small-volume ASIC expensive. Even in the shuttle programsprovided by several foundries, a 5 mm×5 mm chip costs ˜$75,000. Thisprice tag is difficult to accept for most design-houses.

5. Fabrication of Conventional Mask and Master Optical Disc

In the prior art, the fabrication of a conventional mask is similar tolithographic process in IC. First, photoresist is coated on mask blank,and exposed by e-beam. Then the undesired Cr film is etched away. It istime-consuming and expensive. For PGA, ROM and others, the mask-makingshould take advantage of the fact that typical openings in these devicesare regularly sized and spaced. The opening masks for these devices canbe made in a shorter time and at a lower cost.

Optical discs, such as CD, VCD, DVD, have a huge consumer market. Anoptical disc is fabricated by pressing a master optical disc on a discblank. Currently, the fabrication of master optical disc is similar tothe fabrication of mask in IC. It is time-consuming and expensive.

OBJECTS AND ADVANTAGES

It is a principle object of the present invention to provide a low-costlithography.

It is a further object of the present invention to lower the mask cost.

It is a further object of the present invention to lower the cost oflithographic and related processes.

It is a further object of the present invention to lower the cost ofhigh-precision masks as well as improve the lithographic resolution.

In accordance with these and other objects of the present invention, alow-cost lithography is disclosed.

SUMMARY OF THE INVENTION

The low-cost lithography disclosed in the present invention is based ontwo approaches: 1. Use low-precision mask (e.g. nF-opening mask) toimplement high-precision pattern (e.g. opening-related patterns); 2.Improve the mask re-usability (e.g. with programmable litho-systemand/or logic litho-system). To take full advantage of these techniques,“design-for-litho-programming (DFL)” is preferred. Low-cost lithographycan be used in litho-programmable integrated circuits (e.g.litho-programmable SCIC and litho-programmable ASIC), as well as thefabrication of conventional masks and master optical discs. On the otherhand, pattern-distribution enables the mask-repair by redundancy. Itfurther enables highly-corrected mask, which provides higher-ordercorrectional structures for clear patterns on wafer.

1. nF-Opening-Related Patterns and Processes

The present invention discloses means for implementing high-precisionpattern through low-precision (thus low-cost) mask. This approach isparticularly suitable to implement opening-related patterns (e.g.inter-level connection and segmented-line). For inter-level connection,the dimension of the opening perpendicular to the upper metal line iscontrolled by the width of the upper metal line; the dimension of theopening along the upper metal line can be larger than the width of thelower metal line. For segmented-line, the dimension of the opening (i.e.segment-gap) is preferably larger than the width of the metal line.Accordingly, the dimension of the opening used in these patterns can belarger than the width of the metal line it interacts with. Because theminimum metal width is 1F, the opening dimension could be nF, with n>1.In the other words, the nF-opening mask (n>1, feature size>1F) can beused to implement high-precision opening-related patterns (feature size˜1F). It offers the following benefits: 1. With a large feature size,the nF-opening mask costs less; 2. With a large toleration on thepattern shape, the nF-opening mask can be made with low-precision tools,even in-house with a conventional litho-tool; 3. The nF-opening mask cantolerate large alignment errors to the upper/lower-level metal patterns.The associated processing cost is lower.

In the present invention, the inter-level connection manufactured fromthe nF-opening mask is referred to as aiv. During its manufacturingprocess, damascene, particularly dual-damascene technique is preferablyused. Dual damascene can take the form of embedded nf-opening,nF-opening-first-trench-second, trench-first-nF-opening-second. On theother hand, segmented-line can be implemented through litho-“OR” betweenan nF-opening mask and a continuous-line mask.

2. Programmable Litho-System

A programmable litho-system can be used to improve the maskre-usability. Its core technology is a programmable mask. Being a “soft”mask, a programmable mask can adjust the pattern thereon based on a setof configuration data. Accordingly, the configuration data are codedinto an image carrier (i.e. the object that receives the exposure lightin a litho-tool, e.g. wafer, mask blank, or master disc. Unless beingspecifically mentioned, wafer is used as an example).Opening-programmable mask (OPM) is one type of programmable mask that iswell suited to adjust the light intensity at openings.

An OPM comprises at least an opening-defining plane (ODP) and alight-modulating plane (LMP). The ODP defines the final shape ofopenings on wafer; the LMP controls light intensity at said opening.Preferably, the ODP and the LMP are located on separate surfaces. Thisarrangement offers more design freedom, better manufacturability andlonger exposure endurance. The LMP comprises a plurality oflight-modulating cells (LMC). They include liquid-crystal-LMC (LC-LMC),MEMS-type-LMC (MEMS-LMC), and emissive-LMC. The LC-LMC and the MEMS-LMCcan be either transmissive or reflective. The LC-LMC is similar toliquid-crystal display (LCD). The MEMS-LMC comprises at least onemovable element, whose position controls the state of opening (“ON” or“OFF”). Typical movable elements are slider, rotor, roller-shade,digital micro-mirror, and digital light-valve. The emissive-LMC controlslight emission at each cell. The LMC can be built in three-dimension(multi-level) to improve its density. On the other hand, the peripheralcircuit of an LMC preferably comprises a transistor and may usetechnologies developed in SOI (e.g. backside grinding, smart-cut).

3. Logic Litho-System

In a logic litho-system, wafer pattern is generated through a series oflitho-logic operations between mask images. Typical litho-logicoperations include litho-“OR” and litho-“AND”. Litho-“OR” can beimplemented through multiple exposures on a wafer. Litho-“AND” can beimplemented through multiple filterings to the exposure light.

One important consequence of the logic litho-system ispattern-distribution. With pattern-distribution, wafer patterns aredistributed on a plurality of mask, or in a plurality of mask regions ona single mask (a.k.a. pattern-distributed mask). After performing alitho-logic operation to the patterns from these masks (regions), thedesired wafer pattern can be obtained. Pattern-distribution can be usedto improve the mask re-usability. It can further enable the mask-repairthrough redundancy and highly-corrected masks.

In some IC designs, one portion of the circuit is quite mature (maturecircuit), with another often subject to change (volatile circuit). Inprior arts, a small circuit change translates to a costly new order forthe whole mask. On the other hand, with pattern-distribution, the waferpatterns can be distributed on two masks: one for mature circuit (maturemask) and the other for volatile circuit (volatile mask). The maturemask can be used in a number of products—an improvement of the maskre-usability. Moreover, the data amount on the volatile mask istypically small and therefore, its fabrication is much lesstime-consuming and less expensive.

A. Mask-Repair Through Redundancy

Pattern-distribution enables the mask-repair through redundancy. Inprior arts, the defective primary mask (i.e. the mask supposed to carrythe patterns to be formed on wafer) is repaired at the defect sites. Tobe more specific, the defect sites are first cleared on the primary maskthen the correctional structures are formed in the cleared space.Because a typical mask is “feature-dense”, “repair-at-site” will likelydamage the adjacent “known-good” mask features and therefore, iserror-prone. The situation becomes even worse for the OPC-mask and thePSM.

On the other hand, during mask-repair through redundancy, after clearingor darkening the defect sites (depending on the logic litho-operation tobe used), instead of “repair-at-site”, the correctional structures areformed in a redundant mask (region). These redundant patterns can formthe desired wafer pattern through a litho-logic operation with theprimary patterns. Because the correctional structures are formed in aseparate area on the mask or on a different mask, this formation processwill unlikely interfere with other “known-good” mask patterns. As aresult, “repair-through-redundancy” is more reliable and robust. It isparticularly suitable to repair the OPC-mask and PSM. Mask-repairthrough redundancy can improve the mask yield.

B. Highly-Corrected Masks

Another important application of pattern-distribution is in the area ofhighly-corrected masks. In prior arts, because the features are closelyspaced, there is not much space to accommodate higher-order correctionalstructures. This is no longer true to a pattern-distributed mask. Afterpattern-distribution, the feature spacing on the pattern-distributedmask can be much larger than that on a conventional mask. This resultsin less proximity effect and less OPC-computing. Secondly and moreimportantly, the larger spacing between mask features can be used toaccommodate highly-order correctional structures. As a result, even ifthe same litho-tool is used, the highly-corrected masks can achieve muchbetter lithographic resolution. Moreover, the highly-corrected mask canstill be a binary mask. This can greatly simplify the mask fabrication.

4. Design-for-Litho-Programming (DFL)

Ideally, a few general-purpose masks (GPM) can be used in mostlithographic processes. The GPM examples include uniform openingprogramming mask (UOPM) and uniform metal-line mask (UMLM). On an UOPM,all programmable openings have the same size and same spacing,preferably 1F or 2F; on an UMLM, all metal lines have the same width andsame spacing, preferably 1F. To maximize their usage, IC layoutpreferably follows “design-for-litho-programming (DFL)”. One set of DFLrules require that: a. any inter-level connection on a wafer shouldcorrespond to the location of a programmable opening on the UOPM; b. atleast the metal lines inside the programming area has the same width andsame pitch, preferably with a smaller or equal corresponding width thanand equal or half corresponding pitch to the programmable openings onthe UOPM.

5. Composite Litho-System

Composite litho-system combines programmable litho-system with logiclitho-system. Besides programmable SoC and programmable lines, acomposite litho-system enables the deep-sub-μm litho-programming basedon manufacturable OPM. It can also improve the mask yield and offerlonger exposure endurance to an OPM.

The size of typical manufacturable LMC (preferably based on the matureLCD technology) is ˜5 μm. With R (image-reduction ratio of a reductionstepper) 4×-5× and assuming no ODP, the wafer opening could be as largeas 1 μm. This is too large for any deep-sub-μm litho-programming.Fortunately, because the ODP opening is the opening that defines thefinal shape of the wafer opening, a small ODP opening size can make thefinal wafer opening small enough. However, the LMC size still dictatesthe wafer-opening period Pw. With a large Pw (˜1 μm), not all waferopenings can be litho-programmed at once. A practical solution is to usea composite litho-system, where a multi-pass exposure with displacementis adopted (i.e. inter-leaved exposure). In the multi-pass withdisplacement, a first number of openings are first exposed, then adisplacement ΔS is made to the wafer or to the mask before a secondnumber of openings are exposed. By setting ΔS to the Pw for thatdeep-sub-μm node, the Pw requirement can be met. Alternatively, thelitho-tools with large R (e.g. 20) can be used. Another practicalsolution is by twice-imaging (referring to section“Quasi-opening-programmable mask”).

During its usage, an OPM preferably goes through a field inspection toensure a desired pattern is generated. An image sensor can be used forthis purpose. On the other hand, to improve the mask yield, a redundantmask (region) can be used. The OPM is well suited for this purpose.

With separate LMP and ODP, the OPM can endure long-term exposure.Between exposures, the location of the ODP is fixed, while the LMP isdisplaced. As a result, all regions on LMP are evenly heated and thisprolongs the OPM lifetime.

6. Applications of Low-Cost Lithography

Low-cost lithography combines techniques such as nF-opening mask,programmable litho-system, and logic litho-system. It is ideal for thefabrication of litho-programmable integrated circuits (LP-IC). The LP-ICcomprises a plurality of litho-programmable opening-related patterns(e.g. inter-level connections and segmented-lines). It can beimplemented with an UOPM and optionally with an UMLM. In an LP-IC flow,a customer first creates a set of customer data; then s/he sends to thefab an order, which has an order volume; the fab returns with a pricequote. The overall expected revenue for this order, which is the productof the order volume and the price quote, can be smaller than the cost ofthe conventional custom opening-mask set corresponding to saidopening-related patterns (custom patterns). In contrast, in prior arts,the completion of the same order involves making a new set of(conventional) custom masks. The manufacturing cost, including otherprocessing and materials costs, should at least be higher than the costfor these masks. Namely, the overall expected revenue of theconventional (non-litho-programmable) IC cannot be lower than the maskcost.

One example of LP-IC is litho-programmable SCIC (LP-SCIC). In anLP-SCIC, a limited number of custom layers are formed bylitho-programming. The LP-SCIC includes litho-programmable ROM (LP-ROM)and litho-programmable PGA (LP-PGA). Another example ofLP-IC—litho-programmable ASIC (LP-ASIC)—goes even further. In theLP-ASIC, no custom masks (at least no expensive custom masks) are usedfor the back-end interconnects. The LP-ASIC design needs to follow amore stringent ASIC-DFL: in at least one metal layer, metal lines arealigned along a first direction with their width and spacing preferably1F; in a metal layer next to said metal layer, metal lines are alignedalong a second direction with their width and spacing also preferably1F. By repetitively using GPM's such as UOPM and UMLM, all interconnectpatterns are formed. Shared in many LP-ASIC products, the GPM's addlittle cost to ASIC chip.

Low-cost lithography, more particularly OPM, can be used to fabricateconventional masks. Accordingly, this type of conventional mask isreferred to as quasi-opening programmable mask (QOPM). It isquasi-programmable because the configuration data can be easily codedinto the QOPM in-house. After being coded by an OPM pattern, the QOPM isused to generate patterns on wafer. By “imaging twice” (first from anOPM to a QOPM, then from the QOPM to a wafer), the image-reduction ratiofrom the OPM to the wafer is R2 (R=4×−5×, R2=16×−25×). As a result,manufacturable OPM (preferably based on mature LCD with dimension ˜5 μm)can be used to create deep-sub-μm features.\

Low-cost lithography can also be used to fabricate master optical disc.This process is similar to that of the QOPM. Note that pits on themaster optical disc are on a spiral. Between exposures, the disc needsto be rotated and displaced.

7. Business Model

The LP-IC preferably follows an internet business model, i.e. a customersend a set of customer data to the fab through internet. Here, thecustomer data may comprise a file pointer. Said file pointer points to afile in a database, which the fab has fast access to. Once a new orderis received, a new set of configuration data is issued to the OPM andthen coded into the wafers-under-exposure. Accordingly, the customerhave direct, remote, real-time control over the wafers-being-processed.

Using a conventional “hard” mask for coding, the prior-art ROM usuallyonly stores “public” information (e.g. operating system). With theadvent of litho-programming, litho-programmable ROM (LP-ROM) can be usedto store “personal” information. To provide better information security,the LP-ROM data sent to the fab are preferably encrypted. Moreover, adecryption engine and a key storage are preferably formed on the samechip as the LP-ROM. After it is shipped back from the fab, user inputsthe key to enable the chip. Thus, the key is not exposed to any thirdparty, during the chip manufacturing or during the chip usage. Thisguarantees maximum data security.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A-1CB illustrate several opening-related patterns used in priorarts.

FIG. 2A illustrates a preferred nF-opening and its interaction withvarious metal lines; FIG. 2B illustrates the core and peripheralportions of said opening on an nF-opening mask.

FIGS. 3AA-3BB illustrate several preferred aivs.

FIGS. 4AA-4CC illustrate several preferred dielectric structures used inaiv.

FIGS. 5A-5D (including FIG. 5A′) describe several preferred aivprocesses based on the conventional metallization.

FIGS. 6A-6C′ describe several preferred aiv processes based on singledamascene.

FIGS. 7AA-7CE′ describe several preferred aiv processes based on dualdamascene.

FIGS. 8AA-8BC illustrate several preferred programmable litho-systems.

FIGS. 9AA-9BE illustrate the structures and relative placements of theLMP and the ODP in several preferred opening-programmable masks.

FIGS. 10AA-10CC illustrate the structures and peripheral circuits of apreferred liquid-crystal LMC (LC-LMC).

FIGS. 11A-11MD illustrate the structures and peripheral circuits forseveral preferred sliders.

FIGS. 12A-12EC illustrate the structures and peripheral circuits forseveral preferred rotors.

FIGS. 13AA-13CB illustrate the structures and peripheral circuits forseveral preferred hinges.

FIGS. 14A-14EB illustrate the structures and peripheral circuits of apreferred roller-shade LMC (RS-LMC).

FIGS. 15A-15C illustrate the structures of several preferred reflectiveLMC's (R-LMC).

FIG. 16B illustrate the structure and circuit symbol of a preferredemissive LMC (E-LMC).

FIGS. 17AA-17BC illustrate the structures of several three-dimensionalLMC (3D-LMC).

FIG. 18D describe a preferred process flow for a peripheral circuit inan LMC.

FIG. 19C explains the concept of “OR” litho-system.

FIGS. 20AA-20EG illustrate several preferred “OR” litho-systems. FIGS.21A-21C explains the concept of “AND” litho-system.

FIGS. 22A-22B illustrate two preferred “AND” litho-systems.

FIGS. 23AA-23DC illustrate several preferred correctional structures forvias on a highly-corrected mask.

FIGS. 24AA-24BC illustrate several preferred correctional structures forline-spaces on a highly-corrected mask.

FIGS. 25A-25C illustrate a preferred implementation of vias on an SoCchip through litho-“OR”.

FIGS. 26A-26FC describe several preferred implementations ofsegmented-lines through litho-“OR”.

FIGS. 27AA-27DB illustrate several preferred thin-film masks.

FIGS. 28A-28B illustrate two preferred general-purpose masks (GPM).

FIGS. 29A-29BC describe several preferred “design-for-litho-programming(DFL)”.

FIGS. 30A-30CB illustrate several preferred programmable SoC openingpatterns and preferred programmable line patterns.

FIGS. 31AA-31DC′ illustrate several preferred implementations of thelitho-programmable deep-sub-μm openings through litho-“OR”.

FIGS. 32AA-32B illustrate several preferred implementations of thelitho-programmable deep-sub-μm openings through litho-“AND”.

FIGS. 33AA-33FC illustrate several preferred mask-inspection andmask-repair means.

FIGS. 34AA-34BB illustrate a preferred OPM with long-term exposureendurance.

FIG. 35 illustrates a preferred flow for a litho-programmable integratedcircuit (LP-IC).

FIGS. 36AA-36F illustrate several preferred implementations oflitho-programmable ASIC.

FIGS. 37A-37C illustrate a preferred implementation of aquasi-opening-programmable mask.

FIGS. 38A-38CB illustrate a preferred implementation of master opticaldisc.

FIGS. 39A-39BC illustrate several preferred business models for an LP-ICand a preferred litho-programmable ROM (LP-ROM).

For the reason of simplicity, in this disclosure, the figure number witha missing appendix refers to all figures with that appendix. Forexample, FIG. 11 refers to FIGS. 11A-17MD; and FIG. 11M refers to FIG.11MA-11MD.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

1. nF-Opening-Related Patterns and Processes

According to the present invention, low-precision masks (nF-openingmasks) can be used to implement high-precision opening-related patterns(e.g. inter-level connections and segmented-lines).

A. nF-Opening-Related Patterns

Opening-related pattern refers to the pattern at which an opening isformed in the photoresist during its manufacturing process. FIG. 2Aillustrates an opening 50 o. It can interact with metal line 162 (and174) adjacent to it. If the metal lines 162, 174 are on adjacent metallevels, the opening 50 o can form an inter-level connection betweenthem; on the other hand, the opening 50 o can also segment the metalline 162 to form metal segments 162 l, 162 r. Accordingly, inter-levelconnection and segmented-lines are referred to as opening-relatedpatterns. For inter-level connection, Wo, Lo of the opening 50 o can belarger than Dm, Dl of the metal lines 162, 174 (˜1F); forsegmented-lines, Wo of the opening 50 o can larger than Dm of the metalline 162 (˜1F). Namely, the dimension Wo (and Lo) of the opening pattern50 o can be larger than the width Dm (and Dl) of the metal-line patternsit interacts with. Accordingly, the opening 50 o is referred to asnF-opening (with n>1, preferably 2). At the 0.13 μm node, the nF-openingmask can use masks from the 0.25 μm node. Apparently, they are much lessexpensive.

FIG. 2B illustrates the core portion 50 oc and the peripheral portion 50op of the nF-opening 50 o on an nF-opening mask 50 om. During itslithographic process, only the core portion 50 oc needs to be fullyexposed. For the peripheral portion 50 op, there is little requirementon exposure dosage and image fidelity (as will become apparent as FIGS.3AA-3BB and FIGS. 26A-26FC are explained). Without stringentrequirements on the shape of the openings, the nF-opening masks can bemade in-house, even in a conventional litho-tool. That further lowersthe mask cost and shortens the turn-around time. Moreover, it isacceptable to have a large alignment tolerance between the nF-openingmask and the metal-line masks. This can lower the processing cost.

B. Aiv Structures

To differentiate from a conventional 1F-via, the physical opening formedin the inter-level connection based on an nF-opening mask is referred toas aiv. FIG. 3AA illustrates the relative placement of the nF-openingpattern vs. the upper-level metal pattern, and FIG. 3AB illustrates therelative placement of the nF-opening pattern vs. the lower-level metalpattern for two aivs 321 a, 322 a. Because the cross-sectional viewsalong both the length and width directions of an aiv are shown therein,FIG. 3 and figures thereafter choose this aiv configuration toillustrate the invention. Here, the length direction of an aiv isperpendicular to the upper-level metal line; the width direction isalong the upper-level metal line. The nF-openings 321, 322 provideinter-level connections between the upper-level metal line 311 and thelower-level metal line 331, between the upper-level metal line 312 andthe lower-level metal line 332, respectively. The aiv pattern on waferis the intersection of nF-opening pattern and upper-level metal pattern.FIG. 3AC illustrates the cross-sectional view of aivs 321 a, 322 a alongA1-A2. Along the width direction of the aiv 322 a, the aiv width 2 wa isequal to the width 2 wm of the upper-level metal line 312. Accordingly,at this direction, the precision of the aiv pattern is controlled by theupper-level metal mask. On the other hand, along the length direction ofthe aiv 321 a, the aiv length 1 la is equal to the length 1 lo of thenF-opening 321 and it can be larger than the width 1 wl of thelower-level metal line 331. As long as the right edge lar of the aiv 321a (corresponding to the right edge 1 r of nF-opening 321 in FIG. 3AA)does not touch the adjacent lower-level metal line 332, circuitperformance will not be affected much. Accordingly, the layout ofnF-openings is very flexible.

For the nF-openings with n>2, adjacent openings 50 oa, 50 ob can becombined into a merged opening 50 o 2 (FIG. 3BA). It providesinter-level connection for the upper-level metal line 162 and twolower-level metal lines 174, 175. In contrast to conventional vias(where, even if connected to a same metal line, adjacent vias are stillphysically separate), the merged aiv 50 a 2 is continuous (FIG. 3BB). Asa reference, a standalone aiv 50 od (i.e. not merged with other aivs) isalso illustrated in FIG. 3BB. The merged opening 50 o 2 can help furtherlower the mask cost.

In FIGS. 2A-3BB, the inter-level connection is a bipolar connection(i.e. its resistance along both directions is low). It should be notedthat, other forms of inter-level connections can also use the nF-openingmask. Examples include programmable inter-level connection (e.g.antifuse) and unipolar inter-level connection (i.e. its resistance ishigher in one direction than in the other, e.g. 3D-ROM cell). In aprogrammable inter-level connection, aiv comprises an antifuse layer; ina unipolar inter-level connection, aiv comprises a ROM layer (a.k.a.quasi-conduction layer). Similarly, the aiv length in these devices canalso be larger than the width of the lower-level metal line, and the aivwidth can be equal to the width of the upper-level metal line. Theirmanufacturing process can be similar to the (bipolar) inter-levelconnection of FIGS. 2A-3BB.

In aivs and the metal lines they connect (FIG. 3AC and FIG. 3BB), thedielectric between the lower-level metal lines (e.g. 331, 332) isreferred to as lower-level dielectric 400 l; the dielectric between theaivs (e.g. 321 a, 322 a) is referred to as inter-level dielectric 400 a;and the dielectric between the upper-level metal lines (e.g. 311, 312)is referred to as upper-level dielectric 400 m. FIGS. 4AA-4CC illustrateseveral preferred dielectric structures.

FIGS. 4AA-4AB illustrate several preferred lower-level dielectrics 400l. In FIG. 4AA, it comprises a single, uniform dielectric 400 d 0. InFIG. 4AB, it comprises at least two dielectric films 400 d 8, 400 d 9.The dielectric film 400 d 9 typically comprises low-κ dielectric (e.g.silicon dioxide, SiLK). The dielectric film 400 d 8 can be used as anetchstop layer for the inter-level dielectric 400 a. It may comprisesilicon nitride, high-ρ poly- or amorphous silicon.

FIGS. 4BA-4BC illustrate several preferred inter-level dielectrics 400a. In FIG. 4BA, it uses a single, uniform dielectric 400 d 1. In FIG.4BB, it comprises two dielectric films 400 d 2, 400 d 3. The dielectricfilm 400 d 2 can be used as etchstop layer for the dielectric film 400 d3. It comprises silicon nitride, high-ρ poly- or amorphous silicon. Thedielectric film 400 d 3 comprises low-κ dielectric. In FIG. 4BC, theinter-level dielectric 400 a comprises three dielectric films 400 d 4,400 d 5, 400 d 6. Each dielectric film can be an etchstop layer for thefilm located thereon. Examples are: the dielectric film 400 d 5comprises low-κ dielectric; the dielectric films 400 d 4, 400 d 6comprise silicon nitride, high-ρ poly- or amorphous silicon.

FIGS. 4CA-4CC illustrate several preferred upper-level dielectrics 400m. In FIG. 4CA, it uses a single, uniform dielectric 400 d 10. In FIG.4CB, the upper-level dielectric 400 m comprises two dielectric films 400d 11, 400 d 12. The dielectric film 400 d 12 can be used as a hard-maskfor the dielectric film 400 d 11. Examples are: the dielectric film 400d 11 comprises low-κ dielectric; the dielectric film 400 d 12 comprisessilicon nitride, high-ρ poly- or amorphous silicon. In FIG. 4CC, theupper-level dielectric 400 m comprises three dielectric films 400 d 13,400 d 14, 400 d 15. Each dielectric film can be an etchstop layer forthe film located thereon. Example are: the dielectric film 400 d 14comprises low-κ dielectric; the dielectric films 400 d 13, 400 d 15comprise silicon nitride, high-ρ poly- or amorphous silicon.Alternatively, the dielectric film 400 d 13 may comprise siliconnitride, etc; the dielectric film 400 d 15 may comprise high-ρ poly- oramorphous silicon.

C. Aiv Processes

FIGS. 5A-7CE′ illustrate several preferred aiv processes. They can becategorized according to the metallization process. They includeconventional metallization, single damascene, and dual damascene.

a. Conventional Metallization

FIGS. 5A-5D (including FIG. 5A′) describe several preferred aiv processflows based on conventional metallization. After the formation of thelower-level metal lines 331, 332, an inter-level dielectric 400 a isformed above, upon which the nF-opening pattern 340 a is transferred(FIG. 5A). After removing the inter-level dielectric 400 a, a conductivefilm 310 m is formed (FIG. 5B). With another lithographic step, aconductive film 310 m forms upper-level metal lines 311, 312 (FIG. 5C).Then an upper-level dielectric 400 m is filled in and planarized (FIG.5D). FIG. 5A′ is a variation of FIG. 5A. After the nF-opening patterntransfer, a tapered sidewall is formed in the inter-level dielectric 400a′. It facilitates the etch of the upper-level metal lines. The tapersidewall can also be used in other aiv structures.

b. Single Damascene

FIGS. 6A-6C′ describe several preferred aiv process flows based onsingle damascene. After forming an nF-opening in the inter-leveldielectric 400 a, a single damascene step is performed, i.e. a metalplug 400 p is formed in the nF-openings (FIG. 6A). This is followed bythe formation of a conductive film and a lithographic step. Theconductive film is then etched to form upper-level metal lines 311, 312.This etching step may remove a portion of the metal plug 400 p (FIG. 6B)or stop thereon (FIG. 6B′). The last step is the fill-in of anupper-level dielectric and planarization (FIG. 6C, FIG. 6C′).

c. Dual Damascene

Aiv process preferably takes full advantage of dual damascene. Dualdamascene can take the form of embedded nF-opening (FIGS. 7AA-7AF,including FIG. 7AA′ and FIG. 7AE′), nF-opening-first-trench-second(FIGS. 7BA-7BH), and trench-first-nF-opening-second (FIGS. 7CA-7CF,including FIG. 7CE′).

FIGS. 7AA-7AF illustrate a preferred aiv process based on dual damascenewith embedded nF-opening. The name “embedded nF-opening” is derived fromthe fact that the nF-opening pattern is embedded between the inter-leveldielectric 400 a and the upper-level dielectric 400 m. Its process flowis as follows. First, an inter-level dielectric 400 a is formed on thelower-level metal lines 331, 332 (FIG. 7AA). It may use the preferreddielectric of FIG. 4BC, i.e. it comprises three dielectric films 400 d4, 400 d 5, 400 d 6. The nF-opening pattern is transferred to thedielectric film 400 d 6 (FIG. 7AB). Then an upper-level dielectric 400 mis formed. It may use the preferred dielectric of FIG. 4CA. This isfollowed by the pattern transfer of a trench mask 340 b (FIG. 7AC). Thena series of etches are performed: a first etch removes the upper-leveldielectric 400 m and the dielectric film 400 d 5 until the dielectricfilm 400 d 4 is reached (FIG. 7AD); a second etch removes the remainingdielectric 400 d 4 until the lower-level metal lines 331, 332 arereached. Thus, aiv 321 a, 322 a and trenches 311 t, 312 t are formed(FIG. 7AE). At last, a conductive material is filled in and planarized(FIG. 7AF).

Compared with the conventional borderless dual damascene, the aiv length11 a is larger than the width 1 wl of the lower-level metal line 331. Toavoid over-etching the lower-level dielectric 400 l during said seriesof etches, an etchstop layer 400 d 4 preferably covers the top surfaceof the lower-level dielectric 400 l (the preferred dielectric of FIG.4BC), or there is an etchstop layer 400 d 8 along both sides of the topsurface of the lower-level metal line 331 (the preferred dielectric ofFIG. 4AB).

FIG. 7AA′, FIG. 7AE′ illustrate an alternate preferred aiv process withembedded nF-opening. In this preferred embodiment, the inter-leveldielectric 400 a and upper-level dielectric 400 m are both single,uniform dielectrics. Preferably they comprise different dielectrics (forexample, 400 a comprises nitride, 400 m comprises oxide). Otherprocessing steps are similar to those in FIGS. 7AA-7AF.

In FIG. 7A, the nF-opening pattern-transfer occurs between the formationof the inter-level dielectric and the upper-level dielectric. In FIG. 7Band FIG. 7C, all pattern transfers occur after these dielectrics areformed. The difference between FIG. 7B and FIG. 7C is the order in whichthe masks are applied.

FIGS. 7BA-7BH illustrate a preferred aiv process based on dual damascenewith the nF-opening-first-trench-second. First, an inter-leveldielectric 400 a and an upper-level dielectric 400 m are formed on thelower-level metal lines 331, 332 (FIG. 7BA). Here, the inter-leveldielectric 400 a uses the dielectric of FIG. 4BB, and the upper-leveldielectric 400 m uses the dielectric in the first example of FIG. 4CC.Next, the nF-opening patterns 321, 322 are transferred to the dielectricfilm 400 d 15 (FIG. 7BB). The etched dielectric film 400 d 15 can beused as a hard-mask for subsequent processing. Then a pattern-transferis performed to a trench mask 340 b (FIG. 7BC). This is followed by aseries of etches: a first etch removes the exposed dielectric film 400 d14 until 400 d 13 is reached (FIG. 7BD); a second etch removes theexposed dielectric films 400 d 15, 400 d 13 until 400 d 3, 400 d 14 arereached (FIG. 7BE); a third etch removes the exposed dielectric films400 d 3, 400 d 14 until 400 d 2, 400 d 13 are reached (FIG. 7BF);photoresist is then removed and a fourth etch removes the exposeddielectric films 400 d 2, 400 d 13, 400 d 15 until 400 d 3, 400 d 14 arereached (FIG. 7BG). At last, a conductive material is filled in andplanarized (FIG. 7BH).

FIGS. 7CA-7CF illustrate a preferred aiv process based on dual damascenewith trench-first-nF-opening-second. Similar to FIG. 7BA, an inter-leveldielectric 400 a and an upper-level dielectric 400 m are formed on topof the lower-level metal lines 331, 332. Different from FIG. 7BA, thetrench patterns 311, 312 are transferred to the dielectric film 400 d 15first (FIG. 7CA). Then, the nF-opening pattern 340 a is transferred tophotoresist (FIG. 7CB). In addition to photoresist, the dielectric film400 d 15 can be used as a hard-mask. This is followed by a series ofetches: a first etch removes the exposed dielectric film 400 d 14 until400 d 15 is reached (FIG. 7CC); a second etch removes the exposeddielectric film 400 d 13 until 400 d 3, 400 d 15 are reached (FIG. 7CC);then photoresist 340 a is removed and a third etch removes the exposeddielectric films 400 d 3, 400 d 14 until 400 d 2, 400 d 13, 400 d 15 arereached (FIG. 7CD); a fourth etch removes the exposed dielectric films400 d 2, 400 d 13, 400 d 15 until 400 d 3, 400 d 14 are reached (FIG.7CE). At last, a conductive material is filled in and planarized (FIG.7CF).

After finishing said fourth etch of FIG. 7CE, a dielectric spacer 400 spcan be formed on the sidewall of the aiv and the trench (FIG. 7CE′).Said dielectric spacer 400 sp ensures electrical isolation between theaiv and the adjacent lower-level metal line. Apparently, a dielectricspacer can also be used in the damascene structures of FIGS. 5C, 6B,6B′, 7AE, 7AE′, 7BG. In FIGS. 5C, 6B, 6B′, the dielectric spacer isformed along both sides of the nF-opening; in FIGS. 7AE, 7AE′, 7BG, itis formed along both sides of the aiv.

In FIG. 7, there are a plurality of etch-stop layers. In fact, timedetch could also be used. For the timed etch, some etchstop layers maynot be needed in the aiv structure.

2. Programmable Litho-System

A programmable litho-system can be used to improve the maskre-usability. Its core technology is a programmable mask. Being a “soft”mask, a programmable mask can adjust the pattern thereon based on a setof configuration data. The configuration data are coded into an imagecarrier (i.e. the object that receives the exposure light in alitho-tool, e.g. wafer, mask blank, or master disc. Unless beingspecifically mentioned, wafer is used as an example).Opening-programmable mask (OPM) is one type of programmable mask that iswell suited to adjust the brightness of openings.

FIG. 8AA illustrates the flow of customer data 17 from a customer 12 toa fab 14 (e.g. a foundry). The customer data 17 can be encrypted or inplain-text. They are delivered to the fab 14 through a medium 18. Themedium 18 includes internet, hard-disk drive (HDD), optical disc andother means. After necessary data processing in the fab 14, the customerdata 17 are converted into a set of configuration data 16. Theconfiguration data 16 are then hard-coded into the image carrier by theprogrammable litho-system 20.

FIG. 8AB illustrates the hierarchy of a programmable litho-system 20.Its core portion is an OPM 30. An OPM comprises at least anopening-defining plane (ODP) 32 and a light-modulating plane (LMP) 38.The ODP 32 defines the final shape of openings on a wafer, while the LMP38 controls the light intensity at said opening. The ODP 32 comprises aplurality of ODP openings 70 and the LMP 38 comprises a plurality oflight-modulating cells (LMC) 40. Each LMC 40 comprises alight-modulating area (LMA) 50 and a peripheral circuit 60.

FIGS. 8BA-8BC illustrate three preferred programmable litho-system:transmissive, reflective and emissive. In FIG. 8BA, a transmissiveprogrammable litho-system 20 comprises a light source 26, a transmissiveOPM 30 t and a projector 24. After the light passes through the OPM 30t, its intensity varies according to the patterns on said OPM 30 t,which is controlled by the configuration data 16. FIG. 8BB illustrates apreferred reflective programmable litho-system 20. It is well suited forthe litho-system using ultra-violet light (UVL). The light is modulatedby a reflective OPM 30 r before being projected onto the wafer 22. Thereflecting/non-reflecting pattern of the reflective OPM 30 r iscontrolled by the configuration data 16. In FIG. 8BC, an emissiveprogrammable litho-system comprises an emissive OPM 30 e. The emissiveOPM 30 e comprises of a plurality of light-emitting cells. Byselectively turning on or off these cells, the configuration data 16 canbe passed to the wafer 22. The emissive OPM 30 e is similar to themultiple parallel electron guns used in an e-beam litho-system. Besidesoptical light, X-ray, e-beam or ion beam can also be used in theprogrammable litho-systems.

A. Opening-Programmable Mask (OPM)

The OPM preferably has a programmable opening corresponding to everycross-point between vertical and horizontal metal lines in the ROM orPGA. FIG. 9AA is a plan view of a LMP 38. It controls the exposureintensity at openings 70 aa-70 bb (FIG. 9AB). In this preferredembodiment, the LMP 38 comprises a configuration-data bus 16 and a 2×2light-modulating matrix. The light-modulating matrix comprises an arrayof LMC's 40 aa-40 bb, a row-decoder 16 a and a column decoder 16 b. TheLMC is the basic building block of LMP 38. Each LMC 400 aa-40 bbcomprises an LMA 50 aa-50 bb and a peripheral circuit 60 aa-60 bb. TheLMA has a dimension of D_(c), a spacing of S_(c) and a period of P_(c).Its state is controlled by address line 42 a-42 b and data line 44 a-44b. At its “ON” state, the LMA can transmit light (for the transmissiveOPM 30 t) or reflect light to a pre-determined direction (for thereflective OPM 30 r); at its “OFF” state, it cannot. In FIG. 9AA andfigures thereafter, if the crosshatch in an LMA is sparse (as in LMA 50ba), the state of this LMA is un-defined; if the crosshatch is dense (asin LMA 50 aa), this LMA is at the “OFF” state; if there is no crosshatch(as in LMA 50 ab), this LMA is at the “ON” state. FIG. 9AB is a planview of the ODP 32. It defines the final shape of the opening on wafer.Every opening is aligned with and preferably encompassed by an LMA (e.g.70 aa is aligned to 50 aa, referring to FIGS. 9BA-9BE). The making ofthe ODP 32 is a standard mask-making process. It may use the advancedmask-making techniques, such as optical proximity correction (OPC) andphase-shift mask (PSM).

Referring now to FIGS. 9BA-9BE, the relative placements of severalpreferred ODP's and LMP's in an OPM are illustrated. In these figures,because it can better demonstrate the state of the LMC, a movableelement—slider 51 a—is used as example. In most cases, when the slider51 a covers the LMA 50 aa, the LMC 40 aa is at the “OFF” state;otherwise, it is at the “ON” state. In FIG. 9BA, the LMP 32 and the ODP38 are merged and there is no physical distinction between them. InFIGS. 9BB-9BC, the ODP 32 and the LMP 38 are located on separatesurfaces. This arrangement offers more design freedom, bettermanufacturability and longer exposure endurance (referring to FIGS.34AA-34BB). In FIG. 9BB, the ODP 32 and the LMP 38 are located at twosides of the mask substrate 36. In FIGS. 9BC-9BE, the ODP 32 and the LMP38 are located on two different substrates 36 a, 36 b. The preferredembodiment in FIG. 9BD can be used in a reflective-OPM or anemissive-OPM. For the reflective-OPM, the ODP 32 performs lightreflection at each opening 32 r; the LMP 38 can be built on alight-absorptive membrane 36 m. For the emissive-OPM, the emissive plane32 emits light at every opening 32 r; the LMP 38 controls the intensityof light passing through. The preferred embodiment of FIG. 9BE can beused in a reflective-OPM. Compared with FIG. 9BD, the placements of theODP 32 and the LMP 38 are exchanged. The movable element 51 a comprisesa reflective film. Apparently, the LMC in FIG. 9BE may use variouspreferred embodiments of FIGS. 15A-15C.

B. Light-Modulating Cell (LMC)

LMC is the basic building block of an OPM. It adjusts its lightintensity according to the configuration data. It can borrow many designideas and process ideas from the display industry. FIGS. 10AA-16Billustrate the structures and peripheral circuits of various preferredLMC's.

a. Liquid-Crystal LMC (LC-LMC)

Liquid-crystal display (LCD) technology is very mature. It can bereadily applied to the liquid-crystal LMC (LC-LMC). FIGS. 10AA-10ABillustrate a preferred LC-LMC 40. The LC-LMC 40 comprises a switch 60 sand a liquid-crystal LMA (LC-LMA) 50. It is aligned with an ODP opening70 and preferably encompasses it. In FIG. 10AA and figures thereafter,the dashed ODP openings 70 shown in the LMC 40 is actually the projectedimage of the ODP opening 70 on the LMC 40, in the case the OPD opening70 and the LMC 40 are not located on the same plane. The LC-LMC 40comprises two opposing substrates 36 e, 36 f, two opposing electrodes 59p, 59 m, two alignment layers 36 b, 36 d and a liquid crystal layer 36c. For the transmissive cell, there are two opposing polarizers on bothsides of the liquid crystal. To those of ordinary skills in the art,light transmission through liquid crystal can be modulated by a voltagebetween the electrodes 59 p and 59 m. Alternatively, reflective LC-LMCcan be used. Its material and manufacturing are well known in the art.Apparently, the LC-LMA 50 can occupy most area of the LMC 40 (FIG.10AA).

The circuit symbol representing the LC-LMC is a capacitor 50 c 0 (FIG.10B). Its peripheral circuits are illustrated in FIGS. 10CA-10CC. Theperipheral circuit of FIG. 10CA is a dynamic circuit. It uses aDRAM-type circuit 60 dp. When the voltage on the address line 42 risesto high, the switch 60 s is turned on. The corresponding configurationbit 44 is sent to the capacitor 50 c 0 and determines the state of theLMC. FIGS. 10CB-10CC are static circuits. For static circuits, leakagecurrent in the capacitor will not affect the LMC state. This isparticularly useful for long-term exposure (no refresh is needed). Thepreferred circuit in FIG. 10CB is an SRAM-type circuit 60 sp 1. Itcomprises two switches 60 s, 60 sb and an SRAM cell formed by twoinverters 60 i 1 a, 60 i 1 b. Its operation is similar to that of FIG.10CA. The preferred circuit in FIG. 10CC uses a non-volatile-memory(NVM)-type circuit 60 sp 2. It comprises a NVM cell 60 nvm and a switch60 sp. Its operation includes two steps: a programming step and anexposure step. During the programming step (i.e. before exposure), theconfiguration bit is stored in the NVM cell 60 nvm. The switch 60 sp isturned on, and voltages are applied to the address line 42 and theconfiguration-bit line 44. The threshold voltage of the cell 60 nvm isvaried according to the configuration bit. During exposure, thecapacitor 50 c 0 is first discharged. At this time, all address lines 42and the configuration-bit line 44 are grounded with the switch 60 sp on.Then the switch 60 sp is turned off, and the voltages on all addresslines 42 and the configuration-bit line 44 rise to appropriate values.If its threshold voltage is high, the NVM cell 60 nvm is still off andthe capacitor 50 c 0 is not charged; if its threshold voltage is low,the NVM cell 60 nvm is on and the capacitor 50 c 0 becomes charged. As aresult, the light passing through the LMC is modulated.

b. MEMS-LMC

MEMS-LMC can directly modulate the exposure intensity at each opening.At its “ON” state, because the exposure light does not have to pass anyadditional medium, its intensity loss is minimized. The MEMS-basedprogrammable litho-system can achieve comparable throughput to aconventional litho-tool. In addition, because the MEMS structurephysically blocks the light path, the MEMS-based OPM is insensitive tothe wavelength of the exposure light. It can be used in DUV, EUV, X-ray,e-beam, ion-beam and other litho-systems. Examples of MEMS-LMC include:slider, rotor, hinge, roller-shade, digital micro-mirror, and digitallight-valve.

Slider

Slider is a simple MEMS structure with good manufacturability. FIGS.11AA-11MD illustrate various preferred translational light-modulatingcells (T-LMC). Its core element is a slider 51 a. In FIG. 11AA, theslider 51 a is at the “OFF” state, i.e. it covers the opening 70;whereas in FIG. 11AB, the slider 51 a is at the “ON” state, i.e. itmoves away from the opening 70. Being translational, the relativeposition of the four corners WXYZ of slider 51 a does not change duringthe movement.

FIGS. 11CA-11GC illustrate a first preferred T-LMC type. This preferredT-LMC type comprises a floating slider and its driving forces arecapacitive. A first preferred embodiment of the first T-LMC type isillustrated in FIGS. 11CA-11CC. Besides the slider 51 a, it furthercomprises two flange pairs 51 p 1 a/51 m 1 a and 51 p 1 b/51 m 1 b.These two flange pairs cover the outer edge of the slider 51 a. At the“OFF” state, the slider 51 a aligns with the first flange pair 51 p 1a/51 m 1 a. At the “ON” state, the slider 51 a aligns with the secondflange pair 51 p 1 b/51 m 1 b. The cross-sectional view along BB′, CC′are illustrated in FIGS. 11CB-11CC, respectively. Being constrained bythe flange pair 51 p 1 a/51 m 1 a on both sides, the slider 51 a canonly move along the y direction on the surface of the substrate 36. Theinner surfaces of the flanges 51 p 1 a, 51 m 1 a are lined with adielectric 51 b, which prevents electrical shorting between the slider51 a and the neighboring flanges 51 p 1 a, 51 m 1 a.

FIGS. 11DA-11DC illustrate a preferred manufacturing sequence for thefirst preferred embodiment of the first T-LMC type. A first sacrificiallayer 51 s 1 and the slider layer 51 a are formed on substrate 36. Theyare etched to form a first slider stack 51 t 1 (FIG. 11DA). The sliderlayer 51 may comprise poly-silicon or metals such as aluminum. In thecase of poly-silicon, the sacrificial layer 51 s 1 may comprise siliconoxide; in the case of metals, the sacrificial layer 51 s 1 may comprisepolymeric materials (e.g. photo-resist). Then a second sacrificial layer51 s 2 is formed on top of the first slider stack 51 i 1 (FIG. 11DB).Preferably, the second sacrificial layer 51 s 2 is planarized. It maycomprise the same material as the first sacrificial layer 51 s 1.Afterwards, the second sacrificial layer 51 s 2 is etched to form asecond slider stack 51 t 2. This is followed by deposition of dielectric51 b and the flange layer. They are etched to form flange pair 51 p 1a/51 m 1 a (FIG. 11DC). Finally, the slider 51 a is released by removingthe sacrificial layers 51 s 1, 51 s 2 in an aqueous or plasmaenvironment.

FIGS. 11EA-11EB illustrate several alternate preferred embodiments ofthe first preferred T-LMC type. In FIG. 11EA, an insulating spacers 51 cis formed along the vertical edges of the flanges 51 p 1 a, 51 m 1 a. Itprovides better electrical isolation between the slider 51 a and theflanges 51 p 1, 51 m 1. In FIG. 11EB, dimples 51 d are added to theunder-edge of the slider 51 a. They reduce the friction between theslider 51 a and the substrate 36. They can be fabricated by etching,preferably isotropically, a portion of the first sacrificial layer 51 s1 before the slider layer 51 a is deposited. FIG. 11EC further disclosesa preferred embodiment using comb-drives. A plurality of interleavedfingers 51 f 1 a, 51 f 1 b are attached to the slider 51 a. Theyincrease the capacitive driving forces exerted on the slider 51 a. Thus,it would take less time for the slider 51 a to switch position. As aresult, the throughput of the programmable litho-system can be improved.Apparently, further improvement in throughput can be achieved if thecomb-drives and the dimples are combined.

FIG. 11F is a circuit symbol representing the preferred T-LMCillustrated in FIGS. 11CA-11CC and FIGS. 11EA-11EC. It comprises twocapacitors 50 c 1 a, 50 c 1 b. Each flange pair forms a capacitor: theflange pair 51 p 1 a/51 m 1 a forms a first capacitor 50 c 1 a; theflange pair 51 p 1 b/51 m 1 b forms a second capacitor 50 c 1 b. Theslider 51 a is represented by a floating electrode. The capacitors 50 c1 a, 50 c 1 b are out-of-phase: when the capacitor 50 c 1 a is chargedup, the capacitor 50 c 1 b becomes discharged. The slider 51 a is driveninto the charged capacitor. FIG. 11GA illustrates a preferred peripheralcircuit. It uses a DRAM-type circuit and comprises a switch 61 s and aninverter 61 i. FIGS. 11GB-11GC are static peripheral circuits. Exceptfor the additional inverters 61 i, 61 i 1 b between two capacitors 50 c1 a, 50 c 1 b, these peripheral circuits are similar to those in FIGS.10CA-10CC.

FIGS. 11HA-11I illustrate a second preferred T-LMC type. This preferredT-LMC type comprises a floating slider and its driving forces are bothcapacitive and elastic. FIG. 11HA is a first preferred embodiment ofthis type. The driving force for its “OFF” state is provided by theflange pair 51 p 2, 51 m 2. However, the driving force for its “ON”state is an elastic force, which is generated by a spring 51 sp. One endof the spring 51 sp is attached to the slider 51 a and the other to thesubstrate by an anchor 51 sa. After the driving capacitor is discharged,the elastic force of the spring 51 sp pulls the slider 51 a away fromthe opening 70. FIG. 11HB illustrates a second preferred embodiment ofthis type. In this preferred embodiment, a comb-drive is used toincrease the driving force for the “ON” state. FIG. 11I is the circuitsymbol representing the second preferred T-LMC type. It is a capacitor50 c 2 and can use the peripheral illustrated in FIGS. 10CA-10CC.

FIGS. 11JA-11MD illustrate a third preferred T-LMC type. In contrast tothe first two T-LMC types, the slider in the third preferred T-LMC typeis shorted to an external electrical signal. The driving forces for thisT-LMC type are capacitive. It comprises a flange pair 51 e and twoopposing electrodes 51 p 3, 51 m 3 (FIG. 11JA). Limited by the flangepair 51 e, the slider 51 a can only move along the y direction. FIG.11JB is a cross-sectional view of the preferred embodiment along DD′.The T-LMC 40 comprises a base pair 51 g, which provides mechanicalsupport as well as electrical contact to the slider 51 a. To reducefriction, dimples may also be used under the slider 51 a. Compared withother preferred T-LMC types, the inner surface of the flange pair inthis preferred embodiment is not coated with a dielectric. FIG. 11Killustrates the circuit symbol representing the third preferred T-LMCtype. It comprises two capacitors 51 c 3 a, 51 c 3 b in series. Themiddle terminal corresponds to the slider 51 a. FIG. 11L is a preferredperipheral circuit. The two end terminals 51 p 3 and 51 m 3 are tied toVDD and GND, respectively. The voltage on the middle terminal 51 a iscontrolled by the configuration bit 44. This peripheral circuit is adynamic circuit. Static circuits in FIGS. 10CB-10CC can also be used.

FIGS. 11MA-11MD illustrate a preferred process flow of the preferredembodiment in FIGS. 11HA-11HB. Compared with the process flow of thefirst preferred T-LMC type (FIGS. 11DA-11DC), an additional step isperformed to form a base pair 51 g (FIG. 11MA) before the firstsacrificial layer 51 s 1 is formed.

Rotor

FIG. 12EC illustrate various preferred in-plane rotationallight-modulating cells (IPR-LMC). Its core element is a rotor 52 a. Allfour corners STUV of the rotor 52 a can rotate around axle 52 b. Whenthe rotor 52 a covers the opening 70, it is at the “OFF” state (FIG.12A); when it rotates away from the opening 70, the rotor 52 a is at the“ON” state (FIG. 12B).

FIGS. 12CA-12CC illustrate a first preferred IPR-LMC type. Thispreferred IPR-LMC type comprises a floating rotor and its driving forcesare capacitive. The rotor 52 a is anchored to the substrate 36 by theaxle 52 b. It is further extended on two edges to form two fingers 52 f1 a, 52 f 1 b. These two fingers 52 f 1 a, 52 f 1 b act as the floatingelectrodes for two capacitors 50 c 4 a, 40 c 4 b (formed by twoelectrode pairs 52 p 1 a/52 m 1 a, 52 p 1 b/52 m 1 b, FIG. 12CA). FIG.12CB is a cross-sectional view of the floating rotor 52 a and its axle52 b along EE′. Limited by the flange 52 c on the axle 52 b, the rotor52 a can only rotate in the x-y plane. Its inner surface is lined with adielectric 52 d. It provides electrical isolation between the rotor 52 aand the axle 52 b. FIG. 12CC represents the circuit symbol for thispreferred IPR-LMC type. It comprises two capacitors 50 c 4 a, 50 c 4 b.With a voltage on the capacitor 50 c 4 a but no voltage on the capacitor50 c 4 b, the rotor 52 a is driven into the capacitor 50 c 4 a andcovers the opening 70. Accordingly, the IPR-LMC is at the “OFF” state.Otherwise, the IPR-LMC is at the “ON” state. The process flow for thispreferred IPR-LMC type is similar to that in FIGS. 11BA-11BC.

FIGS. 12DA-12DD illustrate a second preferred IPR-LMC type. In thispreferred IPR-LMC type, the rotor is shorted to an external electricalsignal and the driving forces are capacitive. The first preferredembodiment in FIG. 12DA and FIG. 12DB uses straight capacitor electrodes52 p 2, 52 m 2. Their edges are lined with a dielectric 52 d. Itprovides electrical isolation between the electrodes 52 p 2, 52 m 2 andthe rotor 52 a. FIG. 12DC illustrates an alternate preferred embodimentof the second IPR-LMC type. Instead of straight capacitor, it usesfingered capacitor. The electrode fingers 52 f 2 a, 52 f 2 b form twocapacitors 50 c 5 a, 50 c 5 b with the claw-like electrodes 52 p 2 and52 m 2. These fingered capacitors provide more driving forces to therotor 52 a. The circuit symbol representing the second preferred IPR-LMCtype is illustrated in FIG. 12DD. Its peripheral circuits are similar tothose used by the third preferred T-LMC type.

FIGS. 12EA-12EC illustrate a preferred process flow for the preferredIPR-LMC of FIGS. 12DA-12DB. A first sacrificial layer 52 s 1 and a rotorlayer 52 a are deposited on substrate 36. They are etched to form arotor stack 52 t. Then a selective over-etch is performed on thesacrificial layer 52 s 1. Not affecting the rotor layer 52 a, thisover-etch creates an undercut underneath the rotor layer 52 a (FIG.12EA). Afterwards, a second sacrificial layer 52 s 2 is deposited aroundthis structure and etched to expose a portion of substrate 36 (FIG.12EB). This is followed by the formation of a flange layer 52 c and acapacitor finger 52 m 2. To prevent electrical shorting between thecapacitor fingers and the rotor 52 a, a dielectric 52 d is formed aroundthe capacitor finger 52 m (FIG. 12EC).

Hinge

FIGS. 13AA-13CB illustrate various out-of-plane rotationallight-modulating cells (OPR-LMC). Its core element is a hinge 53 a. Thehinge 53 a rotates around a hub 53 h, which is confined by a staple 53b. The four corners of the hinge 53 a are labeled as OPQR. At its “OFF”state, the hinge 53 a lays on the substrate and covers the opening 70(FIGS. 13AA-13AB). At its “ON” state, the hinge 53 a rotates away fromthe opening 70. There are two possibility: a) it rotates ˜90 o from its“OFF” state in the x-z plane (FIG. 13AC); b) it rotates ˜180° from its“OFF” state in the x-z plane (FIG. 13AE) and corners QR move from theright-hand side of OP to their left-hand side (FIG. 13AD).

FIGS. 13BA-13BC illustrate a first preferred OPR-LMC. FIG. 13BA is itsplan view and FIG. 13BB is its cross-sectional view along I-I′. In thispreferred embodiment, the hinge 53 a rotates ˜90° around its hub 53 hwhen it is switched from “OFF” to “ON” state. The hinge 53 a and thestaple 53 b are both located on a base 53 c, which provides electricalconnection to the hinge 53 a. There are two electrodes 53 p 1 and 53 m 1in the vicinity of the hinge 53 a. Besides driving the hinge 53 a, theelectrode 53 p 1 also acts as a stop that limits the degree of the hingerotation. It comprises a post 53 ps and an arm 53 ar. The arm 53 ar isenclosed by a dielectric 53 d. This dielectric provides electricalisolation between the electrode 53 p 1 and the hinge 53 a. The circuitsymbol representing this preferred embodiment comprises two capacitors53 c 6 a and 53 c 6 b (FIG. 13BC). They share one common electrode 53 a.Its peripheral circuits are similar to those of the third preferredT-LMC type.

The process flow of this preferred embodiment is similar to the thirdpreferred T-LMC type. However, after the formation of the staple layer53 b, a third sacrificial layer 53 s 3 is formed on top (FIG. 13BD). Avia is formed inside the third sacrificial layer 53 s 3 and filled witha conductor. After another pattern transfer, the electrode 53 p 1 isformed. Finally, all sacrificial layers are removed and the wholestructure is released.

FIGS. 13CA-13CB illustrate a second preferred OPR-LMC. FIG. 13CA is aplan view and FIG. 13CB is a cross-sectional view along J-J′. In thispreferred embodiment, the hinge 53 a rotates ˜180° from its “OFF” stateto “ON” state. The electrodes 53 p 2, 53 p 2 are more symmetrical. Thecircuit symbol and peripheral circuit for this preferred embodiment aresimilar to those of the first preferred OPR-LMC.

Roller-Shade

FIGS. 14A-14C illustrate a preferred roller-shade LMC (RS-LMC). At its“OFF” state, the roller shade 54 a covers the opening 70 and anchors tothe substrate 36 by a flange 54 f (FIG. 14A). The roller shade 54 afurther comprises at least two thermal layers 54 b, 54 c (FIG. 14B).They have different thermal expansion coefficients γ. A resistor 54 rsits on the top surface of the roller-shade 54 a. When a current passesthrough the resistor 54 r and heats up the roller-shade 54 a, the γdifference between the thermal layers 54 b, 54 c rolls up theroller-shade 54 a (FIG. 14C). Accordingly, the RS-LMC switches to its“ON” state.

The roller-shade 54 a can be modeled as a two-terminal resistor 54 r(FIG. 14D). In its “ON” state, preferably a current runs through theroller-shade 54 a. Being resistive, its peripheral circuit is differentfrom capacitive LMC. A first preferred circuit is illustrated in FIG.14EA. Compared with the DRAM-style circuit in FIG. 10CA, the capacitor50 c 0 is replaced by a PMOS 64 s 2 and a resistor 54 r. The gatevoltage of the PMOS 64 s 2 controls the current flow through theresistor 54 r. Its operation is similar to FIG. 10CA except that theRS-LMC switches to “ON” state when 44 is low. Similarly, the staticcircuits in FIGS. 10CB-10CC can also be used. FIG. 14EB illustrates asecond preferred circuit. It comprises an NVM cell 64 nvm and itsoperation includes two steps. In the first step, the NVM cell 64 nvm isprogrammed by the configuration bit. At this time, the voltage on 64 gis high. This turns on the switch 64 s 4 but turns off 64 s 5. Thus, noprogramming current flows through the resistor 54 r. In the second step,the state of the NVM cell 64 nvm translates to the current flow throughthe resistor 54 r. At this time, 64 g is grounded. This turns off theswitch 64 s 4 but turns on 64 s 5. As a result, appropriate voltages areapplied on the address line 43 and the configuration-bit line 44. If thethreshold voltage of the NVM cell 64 nvm is high, no current will flowthrough the resistor 54 r. On the other hand, if its threshold voltageis low, the cell 64 nvm is turned on and a current will flow through theresistor 54 r. Consequently, the roller-shade 54 a is rolled up.

Reflective LMC

Much progress has been made in the reflective display. Two examples aredigital micro-mirror display (DMD) and digital light valve (DLV). Allthese technologies can be used in reflective-OPM. FIG. 15C illustrateseveral preferred reflective LMC (R-LMC). Preferably, it comprises areflector 55 a. On its four corners are four spring arms 55 sp and fouranchors 55 sa. The cross-sectional views of these preferred embodimentsalong LL′ are illustrated in FIG. 15C, respectively. For DUVapplications, the top surface of the reflector 55 a can be coated withinterleaved silicon-molybdenum layers. The first preferred embodiment(FIG. 15B) is a DMD. By adjusting the voltage on the electrodes 55 p, 55m, the reflector 55 a is tilted. If there is no tilt, the incident lightwill be reflected straight back; otherwise, it will be reflected to adifferent direction. An alternate preferred embodiment (FIG. 15C) is adigital light valve. Here, the reflector 55 a is a membrane. Portion ofthe incident light is reflected from its surface, with another portionbeing reflected by the substrate 36 (or the lower electrode 55 b). Whenthere is no voltage on the lower electrode 55 b, the reflector 55 a isat location 55C; with a voltage applied on the lower electrode 55 b, thereflector 55 a is pulled to location 55D. Through differentinterference, the reflected light changes its intensity.

As mentioned earlier, reflective liquid-crystal can also be used for theR-LMC. Since its substrate is in the optical path, the peripheralcircuit of liquid-crystal-based R-LMC can be built on asingle-crystalline wafer. Meanwhile, the reflector 55 a can be stackedon top of the peripheral circuit. Accordingly, the reflector (LMA) areais close to the LMC area, i.e. the fill ratio is nearly ideal.

c. Emissive-LMC

Much works have been performed on the emissive display. Two examples arevertical-cavity surface emitting laser (VCSEL) and field-emissiondisplay (FED). They can also be used in emissive-LMC (E-LMC). FIG. 16Billustrate a preferred E-LMC. The core element in this E-LMC is a VCSEL56 a. It comprises two opposing electrodes 56 p, 56 m, two opposingBragg reflectors 56 e, 56 f, and p-i-n laser medium 56 c-56 d. The VCSELcan be integrated with TFT's, which act as its peripheral circuit. Theequivalent circuit of a VCSEL is a diode, which is a non-linear resistor(FIG. 16B). Its peripheral circuits are similar to those of RS-LMC. Theycan be built in silicon or GaAs wafers.

C. 3D-LMC

Three-dimensional LMC (3D-LMC) can improve the LMC density. In a 3D-LMC,the MEMS structures are built in multiple levels and can overlap eachother. Thus the spacing between the LMC's can be reduced and the LMC'sdensity be improved. FIGS. 17AA-17AC, FIGS. 17BA-17BC illustrate apreferred 3D-slider and 3D-rotor, respectively.

FIGS. 17AA-17AC illustrate a preferred LMC with 3D-slider. For thereason of simplicity, only the core element of the LMC is shown in thesefigures. In FIG. 17AA, two adjacent LMC's 40 x, 40 y are both in their“OFF” state. Note that the LMC disclosed in the earlier portion of thepresent invention has only one slider. In this preferred embodiment, theLMC 40 x comprises two sliders 51 xa 1, 51 xa 2. Closing from its upperand lower sides, the sliders 51 xa 1, 51 xa 2 cover the opening 70 x.The LMC 40 y has a similar structure. In FIG. 17AB, the LMC's 40 x, 40 yare both at their “ON” state. The slider 51 xa 2 moves towards the lowerside of the opening 70 x, while the slider 51 ya 1 moves towards theupper side. Since they are located at two different levels 51A, 51B, thesliders 51 xa 2, 51 ya 1 can overlap each other (FIG. 17AC). With athree-dimensional arrangement of the sliders, the spacing S_(o) betweenthe openings can be reduced and the OPM can achieve a high density.

FIGS. 17BA-17BC illustrate a preferred LMC with 3D-rotor. Only the coreelement is shown in these figures. In FIG. 17BA, two adjacent LMC's 40x, 40 y are both in their “OFF” state. Note that the LMC disclosed inthe earlier portion of the present invention has only one rotor. In thispreferred embodiment, the LMC 40 x comprises four rotors 52 xa 1-51 xa4. Closing from its four corners, the rotors 52 xa 1-52 xa 4 cover theopening 70 x. The LMC 40 y has a similar structure. In FIG. 17BB, theLMC's 40 x, 40 y are both at their “ON” state. The rotors 52 xa 3, 52 xa4 rotates ˜90° around their respective axles 52 xb 3, 52 xb 4, and therotors 52 ya 1, 52 ya 2 rotates ˜90° around their respective axles 52 yb1, 52 yb 2. Located at different levels 52A-52D (FIG. 17BC), the rotors52 xa 3, 52 xa 4, 52 ya 1, 52 ya 2 can overlap each other. With athree-dimensional arrangement of rotors, the spacing S_(o) between theopenings can also be reduced and the OPM can achieve a high density.

D. Manufacturing of the OPM Peripheral Circuit

The manufacturing of the OPM peripheral circuit (i.e. TFT) may takeadvantage of the techniques developed in SOI (silicon-on-insulator)technology. The performance of the single-crystalline-silicon(sc-Si)-based TFT is better than α- or p-Si-based TFT. FIG. 18Dillustrate a preferred process flow for a sc-Si-based peripheralcircuit. The starting material is an SOI wafer 350SOI (FIG. 18A). Itcomprises a substrate 350 s, a buried oxide film 350 o, and a siliconfilm 350 si. The SOI wafer 350SOI has a first surface 350 us and asecond surface 350 ls. On the first surface 350 us, a quartz substrate352 is thermally adhered to the SOI wafer 350SOI (FIG. 18B). Then thebackside of the SOI wafer 350SOI is ground from its second surface 350ls until the buried oxide film 350 o is reached. This is followed by anetch of the buried oxide film 350 o, which exposes the silicon film 350si (FIG. 18C). As a result, an sc-Si film 350 si is formed on top of thequartz substrate 352. This sc-Si film 350 si can be used as thesubstrate for the OPM peripheral circuit (FIG. 18D). Apparently, othertechnologies developed in SOI (e.g. smart-cut) can also be used to forman sc-Si film on the mask substrate. Besides silicon, othersemiconductor materials can also be used for peripheral circuits.

3. Logic Litho-System

In a logic litho-system, wafer pattern is generated through a series oflitho-logic operations between mask patterns. Litho-logic operation canbe performed between conventional masks, between OPM's, or betweenconventional mask and OPM. Typical litho-logic operations includelitho-“OR” and litho-“AND”.

One important consequence of the logic litho-system ispattern-distribution. With pattern-distribution, wafer patterns aredistributed on a plurality of mask, or in a plurality of mask regions ona single mask. After performing a litho-logic operation to the imagesfrom these masks (regions), the desired wafer pattern can be obtained.Pattern-distribution can be used to improve the mask re-usability. Itcan further enable the mask-repair through redundancy (referring toFIGS. 33CA-33FC) and highly-corrected masks.

A. “OR” Litho-System

FIG. 19C explain the concept of “OR” litho-system. FIG. 19B illustratethe images of mask patterns 88AP, 88BP projected on a wafer duringexposure. FIG. 19C illustrates the final wafer pattern 88OLP after thephotoresist development, which is the union of the mask patterns 88AP,88BP. This litho-logic operation is referred to as litho-“OR”. Duringlitho-“OR”, the reference point OA of the mask pattern 88AP coincideswith the reference point OB of the mask pattern 88BP.

FIGS. 20AA-20EG illustrate several preferred “OR” litho-systems. Thepreferred embodiment in FIG. 20C may need only one exposure pass, whileall others need two exposure passes (without photoresist developmentbetween exposures). The preferred embodiments in FIGS. 20B-20EG areseamless multiple-exposure tools, i.e. mask patterns can self-align toeach other during multiple exposures. It can achieve a higherthroughput.

The preferred embodiments in FIGS. 20AA-20AB use a conventionallitho-tool 120O1. It comprises a single projector. Two exposure passes88EA, 80EB are performed to the same wafer 22. During exposure pass88EA, the image of the mask 88A (i.e. the mask pattern 88AP) isprojected on the wafer 22; during exposure pass 88EB, the image of themask 88B (i.e. the mask pattern 88BP) is projected on the wafer 22; andthe wafer needs to be aligned between exposure passes. After allexposure passes are performed, photoresist is developed in a singlestep.

The litho-tool 120O2 in FIG. 20B comprises two projectors 20A, 20B witha shared stage 21M. A wafer 22 is exposed first to the projector 20A.Then it steps forward and is exposed to the projector 20B. The relativeplacement of the masks 88A, 88B can be controlled in such a way that, ifit is aligned with the mask 88A in the projector 20A, the wafer 22becomes self-aligned to the mask 88B when it steps into the projector20B.

The litho-tool 120O3 in FIG. 20C comprises two projectors 20C, 20D witha 50/50 beam splitter 24 s. Here, half of the light entering the beamsplitter 24 s is reflected with another half passing through. The imageformed on the wafer 22 combines the images of the masks 88A and 88B, asthe image of the mask 88A passes through the beam splitter 24 s; theimages of the mask 88B is reflected by the beam splitter 24 s. In thispreferred embodiment, only one exposure (flash) may be needed. It isacceptable to expose another wafer 22′ at the same time on the otherside 120 d of the beam splitter 24 s. This improves the throughput.

In FIGS. 20DA-20DB, a mask-steppable litho-tool 120O4 is used. Itcomprises one projector. Here, the masks 88A, 88B are placed in amask-holder 88H and their relative placement is fixed. Besides preciselycontrolling the wafer stepping, this litho-tool 120O4 can preciselycontrol the stepping of the mask-holder 88H. Similarly, wafer alignmentbetween exposure passes may not be needed.

The preferred embodiment of FIGS. 20EA-20EG is an extension of FIGS.20DA-20DB. Similar to FIGS. 20DA-20DB, it also uses a mask-steppablelitho-tool 120O5 and comprises one projector. Unlike FIG. 20DA-20DBwhere the mask patterns 88AP, 88BP come from two masks 88A, 88B, in FIG.20EC, the mask patterns 88AP, 88BP come from two mask regions 88A′, 88B′of a SINGLE mask 88. Accordingly, this mask 88 is referred to aspattern-distributed mask. On a pattern-distributed mask, that waferpatterns are distributed over a plurality of mask regions. Note that atleast one mask regions 88A′, 88B′ can nearly fill the full aperture 25of the projector, and the combined range of these mask regions 88A′,88B′ exceeds that of the full aperture 25. Here, the origin OA of themask region 88A′ (also designated as the origin MO of the mask 88) has aspacing S_(x) to the origin OB of the mask region 88B′. With the help ofthe pattern-distributed mask, the control of the mask stepping can besimplified.

The pattern-distributed mask 88 might be larger and heavier than aconventional mask. If gravitational sagging is a concern, a support beam88 s may be added thereunder between the mask regions 88A′, 88B′. Itprovides mechanical support to the mask 88 and will not interfere withthe lithographic process. Note that the support beam 88 s can be used inthe preferred embodiments of FIG. 23AB, FIG. 24AB, and FIG. 33EA. Forthe reason of simplicity, it is not shown in these figures.

The exposure process in the mask-steppable litho-tool 12O5 is similar tothat in FIGS. 20DA-20DB. Two exposure passes 80EA, 80EB are performed.During the first exposure pass 80EA, the aperture 25 is aligned with themask region 88A′, e.g. OA coincides with the origin OO of the aperture25 (FIG. 20ED). Dies 38 a-38 d are exposed one-by-one to the mask region88A′ (FIG. 20EF). Between two exposure passes, the mask 88 makes adisplacement of ΔS (ΔS=S_(x)) along the OX direction. Accordingly,during the second exposure pass 80EB, the aperture 25 is aligned withthe mask region 88B′, e.g. OB coincides with OO (FIG. 20EE). Similar,dies 38 a-38 d are then exposed one-by-one to the mask region 88B′ (FIG.20EG). At the beginning of two exposure passes 80EA, 80EB, the waferorigins WO, WO′ coincide. After exposures, a single development stepforms wafer pattern.

B. “AND” Litho-System

FIGS. 21A-21C explain the concept of “AND” litho-system. FIGS. 21A-21Billustrate the first and second mask patterns 88AP, 88BP. FIG. 21Cillustrates the final wafer pattern 88ALP, which is the intersectionbetween mask patterns 88AP and 88BP. The litho-logic operation isreferred to as litho-“AND”. During litho-“AND”, the reference point OAof the mask pattern 88AP coincides with the reference point OB of themask pattern 88BP.

FIGS. 22A-22B illustrate two preferred “AND” litho-systems. FIG. 22A isa transmissive “AND” litho-system 120A1. It uses two masks 88A, 88B,each having a first and second mask patterns 88AP, 88BP. The exposurelight is filtered by both masks 88A and 88B. Images are only formed inareas where the mask patterns 88AP and 88BP are both clear. FIG. 22B isa reflective “AND” litho-system 120A2. Images are only formed in areaswhere both the masks 88A, 88B are reflective.

C. Highly-Corrected Masks

With the help of pattern-distribution, the feature spacing on a maskbecomes larger. Accordingly, the OPC-computing can be reduced and morecomplex, higher-order correctional structures can be accommodated on themask. This enables highly-corrected masks. FIGS. 23A-24BC illustrateseveral preferred highly-corrected masks.

FIGS. 23AA-23AC illustrate a pattern-distributed mask to implementhigh-density vias and its related lithographic process. FIG. 23AAillustrates the desired via patterns 18SI on wafer. The via shown hereonly means that this is a possible via location. If it is drawn in solidline (e.g. 18 a), the via exists; if it is drawn in dashed line (e.g. 18b), there is no via. Typically, the via dimension D_(v) and spacingS_(v) are ˜1F

To implement the via patterns of FIG. 23AA, a pattern-distributed mask18MS with four mask regions 18D (FIG. 23AB) and a logic litho-systememploying four exposure passes can be used. On each mask region, thereare only a fraction of via patterns. For example, the mask region 18Aonly comprises via patterns 18 e′, 18 g′, 18 m′, 18 o′. An exposuresequence is detailed in FIG. 23AC: during exposure step 1, the origin O1of the mask region 18A coincides with OO, the displacement ΔS of themask 18MS is (0, 0), and vias 18 e, 18 g, 18 m, 18 o are exposed onwafer; during exposure step 2, the origin O2 of the mask region 18Bcoincides with OO, ΔS=(−Sx, 0), and vias 18 a, 18 c, 18 k are exposed(no via at 18 i); during exposure step 3, the origin O3 of the maskregion 18C coincides with OO, ΔS=(−Sx, Sy), and via 18 l is exposed (novias at 18 b, 18 d, 18 j); during exposure step 4, the origin O4 of themask region 18D coincides with OO, ΔS=(0, Sy), and vias 18 f, 18 p areexposed (no vias at 18 h, 18 n).

On the pattern-distributed mask 18MS, the via spacing Sv3 is ˜3F. Thisis three times larger than that on a conventional mask. In general, if apattern-distributed mask comprises n² mask regions, its via spacingcould be (2n−1)× larger than that on a conventional mask. Thepattern-distributed mask provides several benefits: First, the proximityeffect between adjacent features is much less. This translates to lessOPC computing and lower mask cost. Secondly and more importantly, thelarger feature spacing can be used to accommodate higher-ordercorrectional structures, thus enabling highly-corrected masks. Incontrast, these higher-order correctional structures cannot beaccommodated on conventional masks, because the feature spacings onthese masks are much smaller and if these mask features were placed atthe minimum spacing, their correctional structures would overlap. As aresult, even if the same litho-tool is used, the highly-corrected maskscan achieve much better lithographic resolution. Moreover, thehighly-corrected mask can still be a binary mask. FIGS. 23BA-23DCillustrate several preferred highly-corrected masks.

FIGS. 23BA-23BC illustrate a rim-shift PSM. Here, via 18 g′ is azero-order clear pattern and the phase-shifter 18 ps around the via 18g′ is its first-order correctional structure. In prior arts, the widthWCS of the phase-shifter 18 ps (W_(cs) is the spacing between the outeredge of the highest-order correctional structures and the outer edge ofthe zero-order clear pattern) cannot exceed F/2, because the spacing SVbetween adjacent vias could be 1F. This severely limits the design ofthe correctional structures. On a pattern-distributed mask, the viaspacing S_(v3) is much larger (≧3F) and W_(cs) increases by more thanthree-fold (˜3F/2). Accordingly, the phase-shifter 18 ps can be bettersized and better lithographic resolution can be achieved.

With a much larger W_(cs), higher-order correctional structures can beaccommodated. FIGS. 23CA-23CC and FIGS. 23DA-23DC illustrate two masks18A, 18A′ with second-order correctional structures. The second-ordercorrectional ring 18 psa in FIGS. 23CA-23CB is separated from via 18 g′by a spacer film 18 sf. The spacer film 18 sf may comprise chrome,phase-shifter or even just a trench. Although it may comprisephase-shifter, the correctional ring 18 psa in FIGS. 23CA-23CB does notcomprise phase-shifter and it is a clear pattern. Namely, the mask 18Ais a binary mask. Its fabrication is easier and costs less. From theE-field diagram of FIG. 23CC, the E-field 18 psaE from the second-ordercorrectional ring 18 psa nearly cancels out the first-order diffractionmaximum of the E-field 18 gE from the zero-order clear pattern (via 18g′). The final exposure light 18 cE can render a good profile.

The preferred embodiments in FIGS. 23DA-23DB comprises a first-ordercorrectional ring 18 ps′ and a second-order correctional ring 18 ps″around the via 18 g′. In this preferred embodiment, the first-ordercorrectional ring 18 ps′ may comprise a phase-shifter, and thesecond-order correctional ring 18 ps″ may not. From the E-field diagramof FIG. 23DC, the addition of E-field components 18 psE′, 18 psE″ fromthese two correctional structures can almost completely cancel out thefirst-order diffraction maximum of the E-field 18 gE. As a result, thefinal exposure light 18 cE′ can render an excellent profile. In fact,this preferred embodiment is an example of the second-order Fresnelplate.

Besides achieving better via resolution, pattern-distribution canachieve better line resolution. The high-density line patterns 28 a-28 cof FIG. 24AA can be distributed on a pattern-distributed mask 28MS ofFIG. 24AB. Here, only clear patterns, i.e. line-spaces (space betweenlines, a zero-order clear pattern), are distributed. The mask region 28Acomprises line-space pattern 29 a′, 29 c′, while the mask region 28Bcomprises the remaining line-space pattern 29 b′, 29 z′. The exposuresequence follows that in FIGS. 20EA-20EG.

The spacing S_(m3) between the line-spaces on a pattern-distributed maskis much larger than the spacing S_(m) on a conventional mask. It canalso accommodate high-order correctional structures. FIGS. 24BA-24BCillustrate several preferred correctional structures. FIG. 24BA issimilar to FIG. 23BA. Mask 28MSP comprises a first-order correctionalstructure 29 ps (a phase-shifter) along the edges of the line-space 29b′. Its W_(cs) can exceed F/2. Similar to FIG. 23BB, mask 28B in FIG.24BB comprises a second-order correctional structure 29 psa. It is abinary mask. FIG. 24BC is similar to FIG. 23BC. Mask 28B′ comprisesfirst- and second-order correctional structures 29 ps′, 29 ps″.

D. Mask with Improved Re-Usability

Logic litho-system can also improve the mask re-usability. For the ICwith mature circuit and volatile circuit, wafer patterns can bedistributed on at least two masks (or mask regions): one for maturecircuit (mature mask) and the other for volatile circuit (volatilemask). Through litho-“OR”, the desired wafer pattern can be formed. Themature mask can be used in a number of products—an improvement of itsre-usability. On the other hand, the data amount on the volatile mask istypically small and therefore, its fabrication is much lesstime-consuming and less expensive.

a. System-on-a-Chip (SoC)

Many SoC products comprise mask-programmable IC (MPIC). They can beintegrated with other IC to implement many functions. FIG. 25Aillustrates the via patterns 80SOC in an SoC chip (SoC via patterns),which comprises an on-chip MPIC 80 mp and an on-chip ASIC 80 as. Notethat the via patterns in the MPIC 80 mp may change frequently. Here, theSoC via patterns can be formed from two masks (or mask regions): an ASICvia mask 80ASO (FIG. 25B) and an MPIC via mask 30MPO (FIG. 25C). TheASIC via mask 80ASO comprises ASIC via patterns 90 aa, 90 ab, 90 ba, butnot MPIC via patterns 90 bb-90 cc. The MPIC via mask 30MPO comprisesMPIC via patterns 90 bb-90 cc, but not ASIC via patterns 90 aa, 90 ab,90 ba. The desired SoC via pattern 80SOC can be formed throughlitho-“OR” between the ASIC via mask 80ASO and the MPIC via mask 30MPO.Apparently, besides via patterns, other layer patterns in an SoC chipcan be formed in the same way.

b. Segmented-Lines

By changing the locations of segment-gap, e.g. 161 g, the length of thesegmented-lines 161′, 161″ can be customized (FIG. 26A). Thesegmented-lines can be implemented through litho-logic operation on twomasks (regions): a continuous-line mask and a segment-gap mask. FIGS.26B-26C illustrate several preferred implementations.

FIGS. 26B-26C illustrate a continuous-line mask 80M and a segment-gapmask 80G. The line patterns 161, 162 on the continuous-line mask 80M aredark patterns; the opening patterns 161 o, 162 o on the segment-gap mask80G are clear patterns. Their relative position on wafer is illustratedin FIG. 26C. Through litho-“OR”, these two masks 80M, 80G form thesegmented-line pattern of FIG. 26A. By controlling the position ofopenings, the length of each segmented-line can be adjusted according tothe customer's needs. Note that the extension 161 o of the opening 161 oover the line 161 has no effect on the final shape of segment-gap.Accordingly, the shape of the openings 161 o can be quite flexible(referring to FIG. 2B).

A first preferred segmented-line process is illustrated in FIGS.26DA-26DC (along C1-C2 of FIG. 26A). It is based on conventionalmetallization. During the first exposure, photoresist 18 pr is exposedto the continuous-line mask 80M. That exposure exposes everywhere exceptareas 161, 162 (FIG. 26DA). During the second exposure, photoresist 18pr is exposed to the opening mask 80G, when the area 161 (i.e. insidesegment-gap 161 g) is exposed (FIG. 26DB). After development, onlyphotoresist in the area 162 remains.

A second preferred segmented-line process is based on damascenetechnique. In damascene, a trench needs to be formed before themetal-filling. A conventional trench mask 80T (FIG. 26E) iscomplementary to the continuous-line mask 80M and is not suitable forlitho-“OR”. To accommodate the need from damascene, negative photoresistis preferably used during the lithographic process. With negativeresist, the same mask set (i.e. the continuous-line mask 80M and thesegment-gap mask 80G) can be used to form the trench pattern required bydamascene. The associated process flow (FIGS. 26FA-26FC) is similar tothat in FIGS. 26DA-26DB, except that photoresist 18 pr is only removedin the area 162 but remains in all other areas. Apparently, this processflow results in the same segmented-line pattern as FIGS. 26DA-26DC.

E. Thin-Film Mask

Logic litho-system can also be used in thin-film mask (e.g. X-ray mask,e-beam mask). Thin-film mask is built on a fragile thin film (e.g.silicon nitride). In order to improve the mask's durability, supportbeams are desired under the thin-film mask. To accommodate supportingstructures such as support beams, a pattern-distributed mask is to beused, i.e. wafer patterns are distributed over multiple mask regions.Within each mask region, there are invalid exposure areas. These invalidexposure areas contains can be used to build support beams. The finalwafer patterns are formed by performing litho-logic operation on thesemask regions.

FIGS. 27AA-27BB illustrate a first preferred thin-film mask. Itcomprises a first mask regions 135A and a second mask region 135B. FIGS.27AA-27AB are the plan view and cross-sectional views of the first maskregion 135A. Support beam 138 s 1 is built in the first mask region135A. In this preferred embodiment, the area within the support beam 138s 1 is the invalid exposure area. The wafer patterns in the invalidexposure area reside on the second mask region 135B. FIGS. 27BA-27BB arethe plan view and cross-sectional view of the second mask region 135B.The patterns of the support-beams 138 s 2, 138 s 3 complements thepattern of the support beam 138 s 1. Through litho-“OR”, the maskpatterns 137 b′, 137 c on the second mask region 135B and the maskpatterns 137 a, 137 b on the first mask region 135A form the desiredwafer pattern. In this preferred embodiment, there is no mask pattern inthe invalid exposure areas 138 s 1-138 s 3.

FIGS. 27CA-27DB illustrate a second preferred thin-film mask. Comparedwith the first preferred thin-film mask, the invalid exposure area 138 s1′ in the second preferred thin-film mask is defined by the mask pattern138 s 1′, but not by the support beam 138 s 1. Thus, the invalidexposure area 131 s 1′ is more accurately defined. Moreover, there ismore design freedom for support beams. For example, straight supportbeam 138 s 1′ can be used.

4. Design-for-Litho-Programming (DFL)

Ideally, a few general-purpose masks (GPM) can be used in mostlithographic processes. To maximize the usage of the GPM, the IC layoutpreferably follows “design-for-litho-programming (DFL)”.

A. General-Purpose Masks (GPM)

Examples of GPM include uniform opening-programmable mask (UOPM) anduniform metal-line mask (UMLM). On an UOPM, all programmable openingshave the same size D_(o) and same spacing S_(o), preferably 1F or 2F(FIG. 28A); On an UMLM, all metal lines are continuous and have the samewidth D_(m) and same spacing S_(m), preferably 1F (FIG. 28B). Oneadvantage of the UMLM is that it is highly regular and can fully utilizethe advanced mask-making techniques such as alternative PSM. To maximizethe usage of the GPM, the IC layout preferably follows the DFL. The DFLincludes via DFL and metal-line DFL.

B. Via DFL

A preferred via DFL is illustrated in FIG. 29A. It can be used toimplement the SoC via pattern in FIG. 25A. Note that in FIG. 25A, thevia 90 ba is not aligned with its adjacent vias. In order to use theUOPM 30U, the via 90 ba has to be displaced by δ so that it coincideswith its nearest programmable opening 50 ba. Because the spacing S_(o)between programmable openings is ˜1F on the UOPM 30U, δ is no largerthan ˜F/2. Namely, the via DFL has small effect on the via layout.

C. Line DFL

The implementation of segmented-lines requires the alignment of thecontinuous-line patterns 80M and the segment-gap patterns 80G. Thesegment-gap patterns 80G can be generated by an UOPM 30U. Accordingly,the continuous-line patterns, at least the continuous-line patternssubject to programming, can coincide with programmable openings on theUOPM 30U. If the line 166 is wider than 1F (FIG. 29BA), it is preferablysplit into a few sub-lines 168, 169 (FIG. 29BB) or at least a fewsub-lines 166 a, 166 b in the programming area 166 pa (FIG. 29BC). Thewidth of these sub-lines is smaller than or equal to that of theprogramming openings, preferably equal to 1F; the pitch of thesesub-lines is equal to the period of the programming openings, preferably2F Combined with openings 50 bb, 50 cb, the desired segmented-lines canbe generated.

5. Composite Litho-System

Composite litho-system combines programmable litho-system with logiclitho-system. Besides programmable SoC and programmable lines, thecomposite litho-system enables the application of manufacturable OPM inadvanced lithography. It can also improve the mask yield and offerlonger exposure endurance to OPM.

A. Programmable SoC

In the preferred embodiment of FIG. 25C, the MPIC via patterns areformed from a custom opening mask. In fact, it can be created from theOPM 80MPO′ of FIG. 30A. In the ASIC area 80 as, all correspondingprogrammable openings are at the “OFF” state; only in the MPIC area 80mp, the OPM 80MPO′ generates valid opening patterns. Accordingly, theOPM 80MPO′ offers programmability to SoC chips.

B. Programmable Line Pattern

Line patterns can be formed by merging a plurality of square openingsand they can be programmable. FIG. 30BA illustrates a line pattern, i.e.merged opening 50 o 3. It can be formed by a single OPM 30O3 in an “OR”litho-system. To be more specific, it can be formed by multi-passexposures with displacement. Here, two exposure passes are performed andthe OPM 30O3 is displaced relative to the wafer by ΔS between theexposure passes. The first exposure pass forms a first opening 50 oa(FIG. 30BB); the second exposure pass forms a second opening 50 ob (FIG.30BC). These opening patterns are merged to form the desired linepattern 50 o 3. More details on multi-pass exposure with displacementwill be disclosed in FIGS. 31CA-31DC′. The programmable line pattern canalso be used to form gap 166 g in wide metal lines (FIG. 29BA). Asillustrated in FIGS. 30CA-30CB, two exposure passes are performed andthe OPM is displaced relative to the wafer by ΔS between the exposurepasses. The combined openings 50 bb, 50 bb′ cut the wider metal line166.

C. Deep-Sub-μm Litho-Programming Based on Manufacturable OPM

In a composite litho-system, litho-programmable deep-sub-μm features(˜0.25 μm) can be rendered by manufacturable OPM (˜5 μm). FIGS. 31AA-32Billustrate several preferred implementations of the litho-programmabledeep-sub-μm openings through litho-logic operation.

FIGS. 31AA-31AB illustrate a preferred implementations of thelitho-programmable deep-sub-μm openings through litho-“OR”. It uses twoOPM's 30Z, 30W. Each OPM comprises a plurality of LMC's 40 z 1-40 z 3,40 w 1-40 w 3. The LMC 40 z 2 on OPM 30Z is always dark, with anothertwo LMC's 40 z 1, 40 z 3 programmable (FIG. 31AA); The LMC's 40 w 1, 40w 3 on OPM 30W are always dark, with another LMC 40 w 2 programmable(FIG. 31AB). On wafer, the pattern from each LMC's 40 z 1-40 z 3 isaligned to and combined with pattern from each LMC's 40 w 1-40 w 3.Although the LMC 40 z 2 (40 w 1, 40 w 3) is always dark, its counterpartLMC 40 w 2 (40 z 1, 40 z 3) on the OPM 30W (30Z) can still program thecorresponding wafer opening. As a result, every wafer opening is stillprogrammable.

The LMC 40 z 2 in FIGS. 31AA-31AB is always set to dark. This can beeasily accomplished by removing the ODP opening at this “always-dark”LMC 40 z 2. Accordingly, no structure needs to be built for this“always-dark” LMC 40 z 2 and an adjacent LMC can extend into its area.Occupying more area, this adjacent LMC is easier to design andmanufacture.

FIG. 31BA illustrates a preferred LC-OPM 30LOX whose LMC extends intothe adjacent cells. Here, LMC 401 a 3 extends to an adjacent“always-dark” LMC (such as 40 z 2 in FIG. 31AA). If it can extend tothree “always-dark” LMC's, the dimension of this LC-LMC could be2R×P_(wo). For a 0.25 μm opening and a conventional 4× litho-tool, thisvalue could be as large as 4 μm. The LMC of this size is highlymanufacturable and reliable. On the other hand, because the openingsimaged on wafer are separately controlled by the ODP opening 70 la 3,they can still be small and have fine features. FIG. 31BB illustrates apreferred MEMS-OPM 30MOX whose LMC extends into the adjacent cells.Similarly, its LMC can use a larger, more manufacturable movableelements 51 a.

In the preferred embodiments of FIGS. 31AA-31BB, two OPM's 30Z, 30W areused. In fact, one OPM is all needed to form the desired wafer pattern.FIGS. 31CA-31DC′ illustrate two preferred implementations. Theseimplementations are based on multi-exposure with displacement. Thismethod is also referred to as inter-leaved stepping.

The preferred implementation in FIGS. 31CA-31CC′ is based on amulti-exposure with mask displacement. It is similar to FIGS. 20EA-20EB,except that mask in this embodiment is an OPM 38. During the firstexposure pass 80EA, the OPM 38 coincides with the aperture 38A of thelitho-tool, and it has a first mask pattern 38(80EA) (FIG. 31CA). Dies38 a-38 d on wafer 22 are exposed one-by-one to the first mask pattern38(80EA) (FIG. 31CB). The first exposure pass 80EA exposes a first halfof the wafer openings 78 za-78 zh (FIG. 31CC). Their state is determinedby the first mask pattern 38(80EA). At the beginning of second exposurepass 80EB, the OPM 38 is displaced by ΔS (ΔS is preferably equal to themask opening period P_(o)) relative to the aperture 38A, i.e. its originmoves from MO to MO′. Meanwhile, the OPM 38 acquires a second maskpattern 38(80EB) (FIG. 31CA′). The second exposure pass exposes a secondhalf of the wafer openings 78 za′-78 zh′ (FIG. 31CC′). Their state isdetermined by the second mask pattern 38(80EB). Note that, at thebeginning of each exposure pass, the wafer origin WO makes nodisplacement (FIG. 31CB′). With a single development step after allexposures, the desired opening pattern is formed on wafer.

The preferred implementation in FIGS. 31DA-31DC′ is based on amulti-pass exposure with wafer displacement. During the first exposurepass 80EA, the OPM 38 has a first mask pattern 38(80EA) (FIG. 31DA).Dies 38 a-38 d on wafer 22 are exposed one-by-one to the first maskpattern 38(80EA) (FIG. 31DB). The first exposure pass 80EA exposes afirst half of the wafer openings 78 za-78 zh (FIG. 31DC). Their state isdetermined by the first mask pattern 38(80EA). During the secondexposure pass 80EB, the OPM 38 acquires a second mask pattern 38(80EB)(FIG. 31DA′) and a second half of the wafer openings 78 za′-78 zh′ areexposed (FIG. 31DC′). Their state is determined by the second maskpattern 38(80EB). With a single development step after all exposures,the desired opening pattern is formed on wafer. Compared with FIGS.31CA-31CC′, the first and second half openings 78 za-78 zh, 78 za′-78zh′ here switch position. Note that during both exposure passes, the OPM38 makes no displacement; however, at the beginning of each exposurepass, the wafer origin is displaced by ΔS (from WO to WO′), where ΔS ispreferably equal to the wafer opening period P_(w).

FIGS. 32AA-32AB illustrate a preferred implementation of thelitho-programmable deep-sub-μm openings through litho-“AND”. Itcomprises two LMP's 38X, 38Y. On the LMP 38X, the LMA 50 x 2 is alwaysclear, with another two LMA's 50 x 1, 50 x 3 programmable (FIG. 32AA);on the LMP 38Y, the LMA's 50 y 1, 50 y 3 are always clear, with anotherLMA 50 y 2 programmable (FIG. 32AB). During exposure, two LMP's 38X, 38Yand an ODP 32 are aligned to each other. Wafer patterns are formedthrough litho-“AND” (FIG. 32AC). For the “always-clear” LMA 50 x 2, itdoes not modulate light and therefore, does not need peripheral circuit.Accordingly, its peripheral-circuit area can be used by the adjacent LMC50 x 1. FIG. 32B illustrates a preferred LC-LMP 38LAX whose LMA 501 s 3extends into the adjacent peripheral-circuit area. Its LMC is larger andmore manufacturable.

D. Mask Inspection and Repair

During its usage, an OPM preferably go through a field inspection so asto ensure the desired pattern is generated. FIGS. 33AA-33BB illustrate afield-inspectable programmable litho-system. It comprises an imagesensor 30 v. It is placed into the exposure-light path after the OPM 30t is configured but before the wafer 22 is exposed (FIG. 33AA).Preferably, at the location of image sensor 30 v, the image from the OPMpatterns has not been reduced by the litho-tool. Accordingly, the imagesensors 30 v can use larger sensing cells. This will benefit the signalintegrity and lower the sensor cost. The sensed signal 16 v (from theimage sensor 30 v) is compared with the configuration data 16. If theymatch, the image sensor 30 v is removed from the exposure-light path anda wafer 22 is exposed (FIG. 33AB); otherwise, the OPM 30 t needs to bechecked.

FIG. 33BA illustrates an OPM pattern during exposure. Based on theconfiguration data 16, the light intensity on the LMC 50 sa′-50 sd′ arevaried; the ODP openings 70 sa′-70 sd′ define the final shape of thewafer openings. FIG. 33BB is a preferred image sensor 30 v. It comprisesa plurality of sensing cells 70 va′-70 vd′ and a peripheral circuit 16c. The sensing cells 70 va′-70 vd′ can be based on conventionalimage-sensing techniques, such as CCD, CMOS imager. The peripheralcircuit 16 c collects the sensed signal 16 v. During field inspection,the sensing cells 70 va′ is aligned with the LMC 50 sa′ (FIG. 33AA), andpreferably encompasses the pattern 70 pa′ imaged by the ODP opening 70sa′ thereon.

Logic litho-system can be used to improve the mask yield. The primarymask (i.e. the mask that is supposed to form wafer patterns) likely hasdefects. A redundant mask (region) can remedy these defects throughlitho-logic operation. OPM is well suited for the redundant mask(region). FIGS. 33CA-33FC illustrate several preferred mask-repairmeans.

FIGS. 33CA-33CC illustrate a preferred mask-repair means based onlitho-“OR”. In this preferred embodiment, the primary OPM 30 p workswith a redundant OPM 30 r to form the desired wafer patterns. In the“OR” litho-system, each redundant LMC (i.e. the LMC on the redundant OPM30 r, e.g. 40 r) corresponds to a primary LMC (i.e. the LMC on theprimary OPM 30 p, e.g. 40_1). For the non-defective primary LMC 40_2,the corresponding redundant LMC 40 r 2 is at the “OFF” state; for thedefective primary LMC 40_1 (FIG. 33CA), its correctional pattern is nowcarried by the redundant LMC 40 r 1 (FIG. 33CC). Meanwhile, means suchas FIB (focused ion beam) is used to darken the defective LMC 40_1 (FIG.33CB) by, for example, filling a light-absorptive material 51 af to thedefect site 51 ad.

In fact, the OPM can perform self-repair. This involves multi-exposurewith displacement. FIGS. 33DA-33DB illustrate a preferred OPM withself-repair. Here, the LMC 40_1 on the OPM 30 is defective and issubsequently darkened; the LMC 40_2 is non-defective. After a primary(first) exposure 20P, the OPM 30 is displaced relative to the wafer byΔS and a redundant (second) exposure 20R is performed. At this time, theimage of the LMC 40_2 formed on wafer is located at where the image ofthe LMC 40_1 should have been during the primary exposure 20P, and allLMC's corresponding to the non-defective primary LMC's are at the “OFF”state. Because the LMC 40_2 carries the designated pattern for thedefective LMC 40_1, the desired wafer patterns can be formed. The OPMself-repair needs only one mask.

Besides the OPM-repair, non-programmable (conventional) masks can berepaired based on pattern-distribution. In prior arts, the mask isrepaired at the defect sites. Because a typical mask is “feature-dense”,this “repair-at-site” scheme will likely damage the adjacent“known-good” mask features and therefore, is error-prone. It is evenmore difficult to repair the PSM and OPC-masks. The present inventionprovides a “repair-through-redundancy” scheme for the defective mask.After clearing or darkening the defect sites (depending on the logiclitho-operation to be used), instead of “repair-at-site”, thecorrectional structures are formed in another (redundant) region on themask or on a different (redundant) mask. This repair step will unlikelyinterfere with other “known-good” mask patterns. As a result,“repair-through-redundancy” is more reliable and robust.

FIG. 33EA illustrates a pattern-distributed mask 88. It comprises aprimary mask region 88P and a redundant mask region 88R. The primarymask region 88P comprises a plurality of darkened areas 40_1, 40_3.These darkened areas cover the defect sites and are preferably formedby, for example, filling a light-absorptive material 51 af on the defectsites (FIG. 33EB). The redundant mask region 88R comprises a pluralityof correctional areas 40 r 1, 40 r 2. Each correctional area 40 r 1corresponds to a darkened area 40_1 in the primary mask region 88P andit carries the designated patterns for the defect site 40_1 (FIG. 33EC).Through litho-“OR”, the patterns from these mask regions 88P, 88R aremerged and form the desired pattern on wafer. It is to be understoodthat the primary mask region and redundant mask region can be located ontwo masks. Repair-through-redundancy is well suited to repair the PSMand OPC-mask.

Alternatively, the OPM can also be used be repair a non-programmablemask. The advantage of the OPM-repair is that the OPM can be readilyconfigured for the mask-repair purpose. This configuration step can becarried out in a short time. Accordingly, the field-repair for thedefective opening masks becomes feasible.

FIGS. 33FA-33FC illustrate an alternate preferred mask-repair meansbased on litho-“AND”. The primary LMP 38 p comprises a defective LMC40_1 (FIG. 33FA). The defect 51 ad′ is cleared by, for example, a laserbeam or FIB, and therefore, the LMC 40_1 becomes always clear (FIG.33FB). A redundant LMP 38 r′ is aligned with the primary LMP 38 p andthe ODP 32. The redundant LMC 40 r 1′ performs light-modulation for thedefective primary LMC 40_1; and other redundant LMC's corresponding tothe non-defective primary LMC's are always at the “ON” state (FIG.33FC). This method can also be extended to the repair ofnon-programmable masks.

E. Long-Term Exposure Endurance

During long-term exposure, an OPM may become over-heated. FIGS.34AA-34BB illustrate a preferred method to avoid over-heating during thelong-term exposure of an OPM. In this preferred embodiment, the LMP38LAX and the ODP 32 are located on two separate substrates. Between twoexposures 20E1, 20E2, the LMP 38LAX is displaced by MD while thelocation of the ODP 32 is fixed. Accordingly, during two exposures 20E1,20E2 to the LPM 38LAX, the exposure light passes through different LMAareas 41 a, 41 b. Accordingly, each LMA area 41 a, 41 b receives lessexposure-light intensity and the over-heating issue is alleviated.Because the location of the ODP 32 is fixed, the LMP displacement doesnot affect the final pattern formed on wafer.

6. Applications of Low-Cost Lithography

Low-cost lithography combines techniques such as nF-opening mask,programmable litho-system, and logic litho-system. It is ideal for thelitho-programmable integrated circuits (LP-IC). Examples of LP-ICinclude litho-programmable SCIC (LP-SCIC) and litho-programmable ASIC(LP-ASIC). Low-cost lithography can also be used during the fabricationof conventional masks and master optical discs.

A. Litho-Programmable Integrated Circuits (LP-IC)

An LP-IC comprises a plurality of litho-programmable opening-relatedpatterns (e.g. litho-programmable inter-level connections andlitho-programmable segmented-lines). It can be implemented with an UOPMand optionally with an UMLM. In an LP-IC flow (FIG. 35), a customerfirst creates a set of customer data; then s/he sends to the fab anorder, which has an order volume; the fab returns with a price quote.The overall expected revenue for this order, which is the product of theorder volume and the price quote, can be smaller than the cost of theconventional custom opening-mask set corresponding to saidopening-related patterns. In contrast, in prior arts, the completion ofthe same order involves making a new set of (conventional) custom masks.The manufacturing cost, including other processing and materials costs,should at least be higher than the cost for these masks. Namely, theoverall expected revenue of the conventional (non-litho-programmable) ICcannot be lower than the mask cost. Accordingly, the present inventiondifferentiates the LP-IC from conventional IC through their expectedrevenues for a specific order.

One example of LP-IC is litho-programmable SCIC (LP-SCIC). In anLP-SCIC, a limited number of custom layers are formed bylitho-programming. The LP-SCIC includes litho-programmable ROM (LP-ROM)and litho-programmable PGA (LP-PGA). Another example ofLP-IC—litho-programmable ASIC (LP-ASIC)—goes even further. By takingfull advantage of low-cost lithography, its back-end process eliminatesthe needs for custom masks (at least expensive custom masks). Thefront-end layers of LP-ASIC are fully customized, just like aconventional ASIC. This can reduce chip area and realize high-speedcircuit. The back-end design needs to follow a more stringent ASIC-DFL:in at least one metal layer of the LP-ASIC, all metal lines are alignedalong a first direction with their width and spacing preferably equal to1F; in a metal layer next to said metal layer, all metal lines arealigned along a second direction with their width and spacing alsopreferably equal to 1F. By repetitively using the GPM such as UOPM andUMLM, all interconnect patterns can be formed without using custommasks. To accomplish the same task in a conventional ASIC, tens ofcustom masks are needed. Moreover, these GPM's are shared in manyLP-ASIC products, they add little cost to the ASIC chips.

FIGS. 36AA-36AB illustrate two preferred GPM's. FIG. 36AA illustrates a2F-UOPM 30U2 and FIG. 36AB illustrates a 1F-UMLM 80UM (also shown inFIG. 28B). On the 2F-UOPM 30U2, its LMC size D_(o)′ and spacing S_(o)′are equal to 2For at least around 2F The 2F-UOPM 30U2 has bettermanufacturability and can also implement segment-gaps and inter-levelconnections (referring to FIGS. 2A-2B). Alternatively, the 1F-UOPM ofFIG. 28A can be used.

FIGS. 36BA-36BC illustrate a preferred implementation of LP-ASIC usingthe GPM. The interconnects 00 as in FIG. 36BA are the typicalinterconnects encountered in an ASIC layout. They involve two metallevels and include a wide metal line 201 (with width equal to 2F), abended line 203/203′ (its two sections 203, 203′ are connected throughvia 203 v), and a displaced line 202 (the line has a displacement alongthe x direction). A conventional process needs three custom masks, i.e.an upper-level metal mask, a lower-level metal mask and a via mask.According to the present invention, the LP-ASIC only needs two GPM's,i.e. a 2F-UOPM (FIG. 36AA) and an UMLM (FIG. 36AB). FIGS. 36BB-36BCillustrate the LP-ASIC interconnects 00 lp equivalent to interconnects00 as of FIG. 36BA. Here, all upper-level metal lines 00UM are alignedalong the x direction, and all lower-level metal lines 00LM are alignedalong the y direction. For the wide metal line 201 of FIG. 36BA, FIG.36BB uses two 1F upper-level metal lines 211, 212, which are shorted bythe lower-level metal segments 221′, 222′ and a merged aiv 251. For thebended line 203/203′, FIG. 36BB stays the same. For the displaced line202, a conventional ASIC only uses a single lower-level metal line.However, according to the ASIC-DFL, the LP-ASIC segment along the xdirection has to be implemented by the upper-level metal line 00UM (FIG.36BB). Accordingly, the equivalence of the displaced line 202 includesthree metal segments 222″ (OOLM), 214′ (OOUM), 224′ (OOLM), and two aivs253, 254.

To implement the lower-level metal lines 221′-224′ of FIGS. 36BB-36BC,the UMLM 80UM is placed along the y direction in the litho-tool. Torealize the gaps between metal segments 221′ and 221″, 222′ and 222″,223′ and 223″, a first litho-“OR” is performed on the UOPM 30U2(referring to FIGS. 26A-26C). During the first litho-“OR”, the UOPM 30U2has a first opening configuration 230LG (including openings 231-232) andits relative placement to the lower-level metal pattern (including metallines 221-224) is illustrated in FIG. 36CA. Apparently, the openings(e.g. 231) divide the metal lines (e.g. 221) into the segments (e.g.221′, 221″) of FIG. 36BB.

To implement the upper-level metal lines 211-214′ of FIGS. 36BB-36BC,the UMLM 80UM is placed along the x direction in the litho-tool.Meanwhile, to realize the gaps between metal segments 213′ and 213″,214′ and 214″, a second litho-“OR” is performed on the UOPM 30U2. Duringthe second litho-“OR”, the UOPM 30U2 has a second opening configuration240UG (including openings 241-242) and its relative placement to theupper-level metal pattern (including metal lines 211-214) is illustratedin FIG. 36CB. Apparently, the openings (e.g. 241) divide the metal lines(e.g. 213) into the segments (e.g. 213′, 213″) of FIG. 36BB.

Finally, to implement the inter-level connections of FIGS. 36BB-36BC,the UOPM 30U2 is again used. FIG. 36CC illustrates its third openingconfiguration 250O (including openings 251-254) and its relativeplacement to the lower/upper-level metal patterns. These openings (e.g.252) provide inter-level connections between the lower- and upper-levelmetal lines (e.g. 213, 223). Note that all three opening patterns 230LG,240UG, 250O are generated by a single UOPM 30U2.

FIG. 36D illustrates an alternate preferred implementation of wide metalline 201 of FIG. 36BA. It uses a custom metal mask 80CM. The desiredmetal line 201 is formed by performing litho-“AND” on said custom metalmask 80CM and the UMLM 80UM. During litho-“AND”, their relativeplacement is illustrated in FIG. 36D. On the custom metal mask 80CM, themetal pattern 167′ is only needed at places corresponding to the widemetal lines 201 of FIG. 36BA, and its width only needs to be larger thanthe line-spacing 167 s (˜1F). To implement gaps on wide metal line 201,multi-exposure with displacement of FIGS. 30CA-30CB can be used. Sincethe custom metal mask 80CM only contains wide metal lines (>1F), whichcan tolerate large width and alignment error, the mask and processingcosts are fairly low.

The LP-ASIC implementations in FIGS. 36AA-36CC not only can be used in astandalone ASIC, but also in SoC designs with embedded ASIC. FIG. 36Eillustrates a preferred SoC chip 00 with an ASIC block 00 as and aplurality of functional blocks 00 fb. The functional blocks 00 fbusually contains IC blocks with third-party IP, such as memory blocks(RAM, ROM, etc) and processing blocks (CPU, DSP, etc). The SoC patternscan be implemented through litho-“OR” between two mask sets: one for theASIC block 00 as (ASIC mask set), the other for the functional blocks 00fb (functional-block mask set), as in the case of FIGS. 25A-25C. TheASIC mask set follows the LP-ASIC implementations. The functional-blockmask set may be provided by IP-vendors, or may also follow the LP-ASICimplementations.

FIG. 36F illustrates a preferred design flow of LP-ASIC. Similar to aconventional ASIC, it includes steps such as HDL description 00H,netlist extraction 00N, placement 00P, routing 00R, and tape-out 00T.However, the routing 00R of LP-ASIC needs to follow the ASIC-DFL.Moreover, only front-end layout needs to be taped out 00T. The back-endoutput is not layout, but the state or location of openings. It hassmall data amount and can be delivered to the fab through the internet.

B. Quasi-Opening Programmable Mask (QOPM)

Low-cost lithography, more particularly OPM, can also be used tofabricate conventional masks, particularly the conventional mask withregularly-sized and -spaced openings, as in the case ROM, PGA andothers. Accordingly, this type of conventional mask is referred to asquasi-opening programmable mask (QOPM). FIGS. 37A-37C illustrate apreferred process flow.

FIG. 37A illustrates a preferred process flow to fabricate a QOPM froman OPM. It is similar to conventional lithographic process. However, theimage carrier here is not a wafer, but a mask blank 80SP coated withphotoresist (QOPM blank). The QOPM 80SP comprises a plurality of QOPMunits 39 a-39 p. Each QOPM unit corresponds to the exposure field of theOPM during one exposure. In the programmable litho-system, the QOPMblank 80SP steps and the QOPM units 39 a-39 p are exposed one-by-onewith respect to the OPM 30. Between exposures, the OPM patterns areadjusted based on the configuration data. For example, during theexposure 80Ea to the QOPM unit 39 a, the OPM 30 has a first pattern30(80Ea) and the LMC 50 sb is at the “OFF” state (FIG. 37BA); during theexposure 80Eb to the QOPM unit 39 b, the OPM 30 has a second pattern30(80Eb) and the LMC 50 sb is at the “ON” state (FIG. 37BB).Accordingly, on the QOPM 80SP, no opening is formed at location 72 b,and an opening is formed at location 72 b′ (FIG. 37C). Note the shape ofthese openings 72 b′ is controlled by the ODP openings 70 sa-70 sd, 70sa′-70 sd′. Besides simple side-by-side stepping, inter-leaved steppingof FIGS. 31CA-31DC′ can also be used during the fabrication of the QOPM.

From FIGS. 37A-37C, the LMC period P_(o) on the OPM 30 is R times theopening period P_(q) on the QOPM 80SP. If a same litho-tool is used toexpose the QOPM 80SP to a wafer, P_(o) can be R² times the wafer openingperiod P_(w). By “imaging twice” (first from an OPM to a QOPM, then fromthe QOPM to a wafer), the image reduction ration from the OPM to thewafer is R². With a typical R 4×-5×, the LMC can be 16×-25× larger thanP_(w). For example, at the 0.13 μm node, an LMC could be ˜5 μm. The LMCof this size is highly manufacturable and reliable. Moreover, the QOPMopenings have a size of ˜1 μm. The openings of this size can be formedby a conventional optical litho-tool and configured by an LC-LMC (e.g.an off-shelf LCD from the micro-display industry). Accordingly, a QOPMcan be fabricated in-house. It has a short turn-around time and offersbetter user-configurability. In sum, the QOPM is a very practicalintermediate step for low-cost lithography.

C. Master Optical Disc

Low-cost lithography, more particularly OPM, can also be used tofabricate master optical discs. This process is similar to thefabrication of the QOPM, except that the image carrier now is a masteroptical disc 86D. The master optical disc 86D is circular and has spiraltracks. The spacing between each turn of spiral is S_(s) (FIG. 38A).Digital “0” and “1” is represented through the existence and absence ofpits.

An OPM 30DM can be used to fabricate the master optical disc 86D. TheLMC's 50 da-50 dg on the OPM 30DM form an arc (FIGS. 38BA-38BB). Itcontrols the existence of pits within a degree θ on the master opticaldisc. In this preferred embodiment, θ is 90°. Similar to the QOPM, themaster optical disc steps in a programmable litho-tool and is exposedone section after another. At each exposure, the OPM 30DM adjusts itspattern according to the configuration data. During exposure 80EM1, theOPM 30DM has a first pattern 30DM(80EM1) (e.g. the LMC 50 de is at the“ON” state) (FIG. 38BA) and the disc section 86DA is exposed. FIG. 38CAillustrates the position and orientation of the master optical disc 86Dduring the exposure 80EM1. During exposure 80EM2, the OPM 30DM has asecond pattern 30DM(80EM2) (e.g. the LMC 50 de is at the “OFF” state)(FIG. 38BB) and the disc section 86DB is exposed. FIG. 38CB illustratesthe position and orientation of the master optical disc 86D during theexposure 80EM2. Relative to the exposure 80EM1, the master optical disc86D rotates around its origin 860(80EM2) by θ and displaced by ΔS(preferably equal to θ/360°×S_(s)). In this preferred embodiment, atleast four exposures are needed to form the whole master disc.

7. Business Model

The LP-IC preferably follows an internet business model. As isillustrated in FIG. 8AA, FIG. 35 and FIG. 39A, a customer 12 sends a setof customer data 17 to a fab 14 through a medium 18, such as internet.In the fab 14, wafers are preferably constantly exposed in aprogrammable litho-systems. Once a new order is received, the customerdata 17 are processed by a data-processing unit 15 and converted into aset of configuration data 16. The configuration data 16 are issued tothe OPM and then coded into the wafer-under-exposure. Thus, the customer12 has direct, remote and real-time control.

For data which are frequently needed or whose source code the ownerswant to hide from the customers (e.g. copyrighted materials such asaudio/video materials), they can be stored in a database 1 ddb at ornear the fab 14. To select the interested files 1 da, 1 dc, the customer12 sends pointers 1 pa, 1 pc associated with these files (e.g. byclicking a web-page 12 t) and the data-processing unit 15 will fetchthese files from the database 1 ddb. Because the fab 12 can have fastaccess to the database 1 ddb, the upload time is more acceptable.Alternatively, the customer data 17 can be compressed.

Using “hard” mask for coding, the prior-art ROM usually only stores“public” information. Shared by many users, “public” information doesnot need to be encrypted. However, with the advent of litho-programming,litho-programmable ROM (LP-ROM) will more likely store “personal”information. Accordingly, information security will become a concern.FIG. 39BA illustrates the data flow for a preferred secure LP-ROM.Before sending it to the fab, the customer encrypts the customer data 17at an encryption unit 4 e with a key 7 k. Subsequently, only encrypteddata 17 ed are sent to the fab. The fab 14 plainly codes these data intoa LP-ROM chip 9, without any knowledge of their representation. Afterreceiving chip 9, the customer inputs the key 7 k and enables the chip9. As a result, the key 7 k never falls out of the customer's hands andexcellent information security can be achieved during the chipmanufacturing.

Besides high security during manufacturing, it is also desired tomaintain a high security during the chip usage. Preferably, a decryptionengine 4 d and a key storage 7 m can be built on the same chip as theLP-ROM chip 9. Three-dimensional read-only memory (3D-ROM) is wellsuited for this purpose. As illustrated in FIG. 39BB, the 3D-ROM cells101-103 are located above the substrate 00 and they do not occupysilicon real estate. Accordingly, the substrate 00 can accommodate alarge number of transistors 5 and NVM 7. They can be used to form thedecryption engine 4 d and the key storage 7 m (FIG. 39BC). Accordingly,the decryption process can be completely carried out inside the 3D-ROMchip 9. The decrypted data 17 o can be directly forwarded to otherfunctional blocks on the chip, such as D/A converter. During the chipusage, the key is not exposed to the external world and excellentinformation security can be achieved.

While the invention has been particularly shown and described withreference to the preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the spirit and scope of the invention. Forexample, many preferred embodiments use metal lines. In fact, otherconductive lines (e.g. poly-silicon lines) can also be used. Theselow-cost lithography concepts can be readily extended to next-generationlithography (e.g. X-ray, e-beam, ion-beam). The invention, therefore, isnot to be limited except in the spirit of the appended claims.

1. An opening-programmable mask system for forming at least one openingimage on an image carrier, comprising: an opening-defining plane with atleast an opening for defining the shape of said opening image on saidimage carrier; and a light-modulating plane with at least alight-modulating cell for modulating the light intensity through saidopening under the control of a set of configuration data.
 2. Theopening-programmable mask system according to claim 1, wherein saidopening-defining plane and said light-modulating plane are located ontwo separate surfaces or two separate substrates.
 3. Theopening-programmable mask system according to claim 1, wherein saidimage carrier is a wafer, or a mask blank, or a master optical disc. 4.The opening-programmable mask system according to claim 1, wherein saidlight-modulating cell is a light-modulating cell selected from a groupincluding liquid-crystal light-modulating cell, MEMS light-modulatingcell, emissive light-modulating cell and three-dimensionallight-modulating cell.
 5. The opening-programmable mask system accordingto claim 4, wherein said MEMS light-modulating cell further comprises atleast one of the following (A)-(C) structures: (A) an MEMS structureselected from a group including slider, rotor, hinge, roller-shade,digital micro-mirror, and digital light-valve; or (B) an electricallyfloating MEMS structure and/or an electrically shorted MEMS structure;or (C) a capacitive driving structure and/or an elastic drivingstructure and/or a thermal driving structure.
 6. Theopening-programmable mask system according to claim 1, wherein saidlight-modulating cell comprises a peripheral circuit having at least atransistor.
 7. The opening-programmable mask system according to claim1, further comprising means for forming at least a first and secondplurality of opening images on said image carrier under the control ofsaid configuration data, wherein said first plurality of opening imagesinterleave said second plurality of opening images.
 8. Theopening-programmable mask system according to claim 1, furthercomprising means for changing the relative placement between saidopening-defining plane and said light-modulating plane.
 9. Theopening-programmable mask system according to claim 1, furthercomprising means for sensing and inspecting the opening images formed bysaid light-modulating plane.
 10. A logic litho-system, comprising: astage for holding and moving an image carrier in a controlled manner; afirst mask region for forming a first image on said image carrier duringa first exposure; and a separate second mask region for forming a secondimage on said image carrier during a second exposure; whereby said firstand second images interleave.
 11. The logic litho-system according toclaim 10, wherein photolithographic alignment is performed only onceduring said first and second exposures.
 12. The logic litho-systemaccording to claim 10, wherein photoresist development is performedafter said first and second exposures.
 13. The logic litho-systemaccording to claim 10, wherein said image carrier is a wafer, or a maskblank, or a master optical disc.
 14. The logic litho-system according toclaim 10, further comprising: a mask comprising said first and secondmask regions; and means for moving said mask in a controlled manner. 15.The logic litho-system according to claim 10, further comprising: afirst mask comprising said first mask region; a second mask comprisingsaid second mask region; a mask-holder for holding said first and secondmasks; and means for moving said mask-holder in a controlled manner. 16.The logic litho-system according to claim 10, further comprising: afirst projector holding a first mask comprising said first mask regionand performing said first exposure; and a second projector holding asecond mask comprising said second mask region and performing saidsecond exposure; wherein photolithographic alignment is performed onlyonce during said first and second exposures, and photoresist developmentis performed after said first and second exposures.
 17. The logiclitho-system according to claim 10, wherein: said first mask region is aprimary mask region having at least a defect site; and said second maskregion is a redundant mask region having a correctional structure forsaid defect site.
 18. A litho-programmable integrated circuit (LP-IC),comprising at least a litho-programmable layer having a plurality ofopening-related patterns, wherein said opening-related patterns aredefined by a set of customer data and no conventional customopening-mask set is used to form said opening-related patterns duringmanufacturing.
 19. The LP-IC according to claim 18, wherein a method forforming said opening-related patterns includes the steps of: A) sendingan order with an order volume for said LP-IC to a vendor; B) receiving aprice quote for said order from said vendor; wherein, the overallexpected revenue for said order, being equal to the product of saidorder volume and said price quote, is lower than the price of aconventional custom opening-mask set to form said opening-relatedpatterns.
 20. The LP-IC according to claim 18, wherein a method forforming said opening-related patterns includes the step of sending saidcustomer data to said vendor through a medium, said medium includinginternet, disc, and hard-disk drive.